I’m on a random app and while it’s obvious if I pay attention. I, occasionally, tap the down arrow by mistake while scrolling. Usually when I do this I notice it and undo it, but I imagine it’s happened a few times without me noticing.
Just saying it’s possible it’s some donkey like me that fat fingered a downvote.
Every once in a while I'll accidentally bump an upvote or downvote as I'm scrolling. I think I usually catch it but I'm assuming that I've left downvotes on plenty of entirely normal comments when I don'tcatch it. Whenever I get a random downvote I just assume it's from the same thing.
If you maintain an account on an instance that does not hide the identities behind votes, like Kbin, it's a simple thing to know. I don't usually look, but occasionally I'm curious.
EDITED TO ADD: I just looked at Kbin, they do not appear to be showing downvotes anymore (every post and comment on my page has a downvote total of zero) so scratch that, lol
I've never asked. It's happened twice to me on Lemmy: once it was readily apparent because they tangled with me and I guess I really pissed them off, and the other time it was someone I'd never openly interacted with at all. In neither instance was a question going to get more of an answer than I already had, IMO.