Why would it? Seems like a perfectly reasonable and professional response by yishan, shows investors that he isn't going to take crap from ex-employees trying to bad mouth the company.
The person posting the AMA seems to lack the experience needed in dealing this this sort of thing and could of used a bit of help understanding the realities of work life. It is very reasonable to believe that he was angry on being let go but this is a life lesson and I hope in the future he is able to handle things better.
And placing it as a reply in the relevant thread is exactly what you'd do if you believe Reddit threads are a serious, important, and often-canonical source of information. That genuine belief is essentially a requirement to lead Reddit.