The kid is barely 18. The emotion and stress resulting from mistakenly sending a notification to 400,000 is likely overwhelming. Now his real name is going to stay at the center of the internet for a while thanks to being 1st on HN. I would definitely not have coped well with that much internet attention at his age. Some Github replies are more immature than the initial action and I hope he does not receive any threat.
I hope the Epic developers reach out to him nicely with constructive feedback and maybe a thanks for his well-meaning PR.