As in, “person” and “one” were once sort of the same idea, the way we say someone/somebody, etc.
Both words come from Old Japanese. Near as I can tell from reading over Wiktionary, determining etymological links from Old Japanese is troublesome, since Old Japanese is, by definition, pre-historical (i.e. they didn’t develop writing until they brought over kanji from China). Wiktionary has this page, which lists the readings together, but doesn’t really make any connections between them.
But it sounds plausible!
Aye, I’ve been reading up on reconstructed linguistics. An example given by Wiktionary is that English, Lithuanian, Hittite, Latin, Oscan, Old Prussian, Sanskrit, Tocharian A, Gothic, and dozens of other languages all have a word for the number seven that sounds kinda like “seven”, so linguists can infer that there must have been a proto-Indo-European language which was an ancestor of all of these languages, which also had a similar-sounding word for seven, even though noone ever wrote it down at the time. (Or, indeed, wrote anything down at the time.)
So, do similar readings in Old Japanese have similar origins? Well, we don’t know for sure. But probably.
Though it’s also possible that the ひと reading of 一 developed alongside the ふた reading of 二.
Well, my uninformed opinion is that they were/are the same word, but when Kanji was adopted and mapped to Japanese words, the “person” shade of ひと got assigned 人, and the “one” shade of it got assigned 一. It just so happens 一 is only very rarely used.
It’s just too convenient that these would have the exact same reading, very similar meanings (one and person), but have developed from different roots. In my amateur and totally unintelligent opinion, the person shade of ひと is probably more primitive, since “person” is a more primordial concept than numerals, just by a hair. And the number one became ひと as a metaphor to person.