I don't want it to sound like you are being dishonest about this, and it's possible there were things going on in Yishan's head that you were not aware of, but "a new team at reddit" in 8 days makes it a bit hard to believe this came completely out of nowhere.
That's called contingency planning. After getting an investment of $50M I'm pretty sure they did their homework on this and having the CEO resign simply triggered a series of pre-defined steps. You don't get that kind of investment without having at least the basics in place. (Or at least, you shouldn't...).
i too doubt this was the only thing that suddenly made him resign. there has to be more that went on behind the scene that even altman is not talking about...