@forforith ; Yo I've been called boy many times while I didn't even try to look like a boy (sad, well it was grannies tho so I'll just convince myself that they were blind af). It can especially happen for childs or teens, since they aren't fully developped.
A boy can be buffy or can be little and "puny" (I've got some asians friends between 19 and 21 who are "puny" (two of them actually cosplayed as maid traps for the Otakuthon and dude it was so funny, they shaved themself all and I used makeup on them and I swear they looked like girls lmfaooo (tho something was a little weird but they did look like girls), they were 17 at that time)
Plus, it's just a manga story. Doesn't have to be the truth so well just enjoy the story