Some have speculated based on the changes that it was not a well-meaning PR, that it was just an attempt to game the system (similar to what hordes of people do on Hacktoberfest). Of course it's hard to know
Does it actually matter? Like even if the PR is bad / the request to merge was demanding, I don’t think that justifies the response, which I guess was roughly the expected response to a the PR times 400k (plus network effects). I’m not convinced that the people responding can use the same excuse for their immaturity but maybe they should not be expected to be mature given the trivial requirements for becoming members of that org.
Speculating or repeating speculations on why he did this is not moving the ball forward at this point. It has been a harmless event so far. Github is now aware of an issue that would have come up eventually anyway and they can add future warnings when notifying >10,000 people, Epic can update the structure/permissions of their Github org, and the kid can keep his passion for tech intact. Win-win-win.
But also, this is a random comment thread on an unrelated site, no one here needs to "move the ball forward". Let people speculate, it makes no fucking difference.