No problem at all, I'm a senior in English so I'm a massive dweeb for these kinds of conversations! (Also don't worry this all still made sense to me!)
I completely missed the afterword I can't lie (I was playing all of the games one after the other on call with a friend so I didn't read the credits too well, that's my bad!). That definitely rules out the ending being something like suicide, but I think running away or contacting someone who can help (in a more positive light than I was originally thinking of) is still pretty plausible!
As for the kid not doing anything intense to potentially get in trouble, I'm looking at this beginning again and I read "you don't know what triggered it" as the "it" being the meltdown. I say meltdown, because as I'm rereading it, this is ringing autism bells in my head due to the passages following it: that the mother doesn't like it when the kid shuts down, goes quiet, doesn't look at her face, doesn't seem to listen, all of this being highlighted in red text... those are like, textbook autism symptoms (and potentially ADHD as well but I am not as well informed in that realm since that's not my personal diagnosis). Also, what may seem as normal for someone who's autistic or neurodivergent in general may seem strange, out of the ordinary, or even offensive to someone neurotypical*, so the kid is a tiny bit unreliable in this sense without the context of what actually went on. If it wasn't a meltdown (which it isn't specified and I agree with you that it's just as plausible that your reading of that sentence is correct and the poor kid didn't actually do anything that intense), I feel like it may have been something a little too blunt or rude, "talking back" when the kid was just trying to be honest, which would explain why the kid doesn't seem to understand in your reading.
EDIT: Wait I just read a bit further and the kid does mentions that they didn't know what happened. Disregard that about the meltdown!
As for the mother, I 100% agree that she's not well adjusted and that it could be both things at once. After all, well-adjusted parents know better than to be abusive. Quick-to-anger parents can do this sort of thing to any kid, and the mental effects of anxiety and self-doubt can happen to any kid being abused as well, so the non-neurodivergency reading is very understandable! And yeah the bathroom break thing, if I may break from my mostly semi-respectful explaining here, is super fucked up and I hope she explodes for that.
But yeah, no problem at all! Thanks for replying, I didn't expect such a well thought-out response and I'm so glad I got one because I love yapping about these things :)