Why don’t you mail the site admin to ask them about it?
EDIT: My rikai extension gives me data on this ghost kanji, too. So, it’s not jisho’s fault
Jisho and rikai are using Jim Breen’s Dictionary file, so the same thing @Ninkastmin shared. (And sure enough they all say the same thing)
I totally forgot about JMDICT for a moment 
So, where do these readings come from, anyway?
EDIT: Looking at the list of ghost kanji in the Japanese Wikipedia, they all seem to have entries in Jim Breen’s dictionary
I looked up a few more kanji, and I got an interesting note on 彁:
音義未詳。音読みは便宜上「カ」「セイ」とされています。
So, I guess the readings in unihan are of the same nature: someone unilaterally decided on some reading to make it easier to look up. Crazy!
The reading か is regular, 哥 gives the reading (like in 謌, 歌) [also the lip ring 可]. No idea where the せい is coming from, though.
All the ghost kanji are regular (follow the construction rules), so while no one is using them they are still kanji. 彁 is something related to bows/strings with reading か. No one needed that in the past, but when enough people attach a meaning and vocab it is as alive as all the other kanji 
Well, yeah, I figured where カ was coming from as well, but the セイ seems random to me. Also, regular or not, that’s still an arbitrary decision, even if it follows the KISS (Keep It Simple, Stupid!) principle. It would have been just as good to give them all the reading ユウレイ or something that does not exist otherwise (I’m a fan of アアア myself). It takes a lot of space bar to get to those characters (as it should be, obviously).
Uh, so wait, why is 妛 read as シ, then?
No idea, it depends on how you read 㞢 (could also be し from the right upper part in 媸). Is this a ghost kanji? Jigen even lists Middle Chinese and rhyme tables and stuff (https://jigen.net/kanji/22939).
Yep, it’s the poster child of ghost kanjis.
The story behind it’s creation is given in the first link, but tl;dr: they wanted to make the kanji 𡚴, so they cut out 山 and 女 and glued them on a piece of paper, then used a copy machine. The line of the cut was mistaken as a stroke.
What! But, how? Or maybe it’s from co-evolution? As in that character legitimately exists in Chinese, but not in Japanese? Interestingly, the correct Japanese character is given in there as an alternative form.
That does explain the existence of a reading, though. I guess they just adapted the Chinese one, since it existed already. I will check some of the other weird ones.
Edit: Oh, wait, nevermind, I just saw that it says 国字, so not Chinese then. But then I can’t explain where they got any of those data from.
I think in the end things got mixed together, their mistake was then to have a mountain hover over a line, while the Chinese character has a connection in 㞢.
It’s strange though, it can’t be 国字 and have that information at the same time …
I think they took it from the variant character 媸 (or made that a variant character) by “virtual deletion” of 虫. It shares kunyomi and meanings. [Edit: so something similar existed in Chinese, and they copied over all data and treated it as a variant.]
Why did they want to make 𡚴? It’s not used either 
There’s a place in 滋賀県 called 𡚴原
From the article:
妛 was an error introduced while trying to record “山 over 女”. “山 over 女” occurs in the name of a particular place and was thus suitable for inclusion in the JIS standard, but because they couldn’t print it as one character yet, 山 and 女 were printed separately, cut out, and pasted onto a sheet of paper, and then copied. When reading the copy, the line where the two little pieces of paper met looked like a stroke and was added to the character by mistake.
Google maps doesn’t know about it.
Poor place, they couldn’t write their name, and now their kanji is not even included in kanjidict while the mistake made it there completely with readings and meanings. 
あけんばら? [Edit: the mistake doesn’t even have the intended reading 
]
Here’s a blog post of someone who went there:
https://blogs.yahoo.co.jp/supopopo_pop/37091557.html
Apparently, no one lives there on a regular basis anymore, but it’s not completely abandoned yet.
Yeah, I’m not sure, but looking at the pictures I don’t think it was a booming center of activity, even at the time when they made the standard. I’m pretty sure that place never saw a computer. (Except for the blogger’s smartphone, I guess)
At the same time, they had a lot of space (in the standard), I’m sure they thought “might as well put it in”. And then, the ghost version got popular from being, well, a ghost kanji. Googling the place, I got more hits with the incorrect kanji 妛原 than with the correct one
In 20 years, that place will be gone, and we will only have a story 
Yeah, this is crazy stuff… I’d like to be a fly in the wall when they were deciding on the ghost readings. I wonder how the decision was made… However, the fact they have convenience readings means that there exists a pool of unused kanji available, complete with readings and (according to some) meanings, which can be used anytime to form new words.
Just for reference, which 電子辞書 model are you using?
Interestingly, as of the time of writing, Google Translate outputs ‘A’ when faced with most ghost kanji 
Actually, just the (chinese) character input of my iphone + kanji.jitenon.jp
I… cannot navigate this site yet
Ah, a fair point.
The search bar is at the top.
You can enter either single kanji, or jukugo (and it will pick up individual kanjis).
The yellow button is 検索 (search). You don’t have to care about the options.
Then, it will give you a list of results (all kanjis you put in, in the basic use).
Click the link looking like 「something」について, and it will take you to the page of that particular kanji.
Finally, you will have to scroll a bit, since it puts navigation links and adds in the way, but you will eventually get a large print of the kanji, followed by its list of radicals, number of strokes, on/kun yomi, meaning, level of kanken, its JIS level and unicode err code.
Hope it helps