It was a direct order from Paul Graham. He keeps mum about it but I have trusted sources who know the truth. Additionally, it's sort of public knowledge:
https://www.washingtonpost.com/technology/2023/11/22/sam-alt...
I don't have a full view into exactly why he was fired from both OpenAI and Y-combinator. But from what I hear the reasoning is a bit similar. Sam Altman is a bit of a political snake. He lacks ethics and he's not honest either. The last part is just me speculating on a lot of the anecdotes from quips I've heard over the years from people who know Sam.
Sams public persona is very different. And I think a lot of HN viewers worship that public persona. But Sam being a darling of the HN and Ycombinator themselves? No way. They fired him so it's unlikely.