I think Explosive Guy basically figured it out through incidental hints before Deku outright admitted it, if I recall correctly. As I remember it Deku only stated it because Baku put him against the wall about it.
In general, and I must admit my memory is very fussy, but my
feeling of how I remember it going is that while the kids doesn't seem to notice anything several adults have at least recognised
a similarity, even if they don't draw any further conclusions. I seem to remember Mightymight even speaking about it with someone at some point, but I might be mixing who it was with up with one of the few peoples who are in on how the power works.
In related news, I recently got told many of the characters names are puns of sorts. It's s shame they don't translate well.
As for anime in general, I've been sort of binging on Attack on Titan recently (yes, I know, give hundred years after everybody else stopped talking about it, as usual). I like it so far.
I'm not particularly fond of how it handles side characters though. I mean, it's clear from the start that it wants to be a "no character is safe!" kind of show, so I went in thinking it would be. But it still feels like there is this huge gap-of-risk between the "core characters" (not just the main characters but the most prominent supportive cast too) and everybody else. And it sort of ruins the suspense when you know that there's no chance at all that any of the newest characters introduced is going to last long at all because the show still wants to kill off *actual* characters, not just unknown faces. I'm a bit into season 2 now and if I remember correctly I don't think a single non-core character introduced is still alive at this point, while only two characters who I felt belonged in the "core" has died.
I do think that in an episode or two that's going to be three, though (it's been stacking up the implication-by-narrative-convention pretty heavily against one guy, so I have strong feelings he's going to due, but likely in a heroic sacrifice or something), so two is not entirely fair. But still.