Today I got a message during reviews telling me I may have made a typo in my Japanese, offering me a chance to correct it. The message was right and the typo was an easy fix. I can’t recall having had that message before. Normally a typo simply counts as wrong.
If this is new software, I applaud it.
I think this feature is fairly old, it’s just a small window of error between a perfect match and an unacceptable deviation from the target word. It does happen more easily with larger words or terms, and since level 1-10 words are usually on the smaller side, maybe that’s why you saw it for the first time today 
There’s also a secret white list with words that are accepted, but not taught. So if you feel your typo wasn’t that much worse than typos in the past, it could be you were actually closer to one of those secret whitelist words.
Thank you. It was a relatively long word お客さん, where the first k didn’t register in the typing. I wish they’d do bit more of that (although I expect they’d still blacklist rendaku failures, one of my bêtes noires).
Oh wait dip, I completely read over the part where this was a correction for the Japanese reading. I believe that is a bit more recent but still somewhere in the past few years iirc. I think they do that through a special whitelist option as well. They even have a blacklist of accidentally typing out the Japanese reading in the meaning part.
my understanding was that it only happened when there should or shouldn’t be a small kana 
ゃ in this case, but also for ょ, ゅ, andっ
potentially also for ん
so yours was supposed to be small, but because you missed the k, it wasn’t
of course, i could be wrong, but i’m sure i’ve typoed longer words and it counted them wrong