If I understand the history correctly, Yishan (the former Reddit CEO) is talking about himself when he talks about a CEO in this story, and so Yishan's post is a brag, with a thin denial tacked on at the end. That's why I believe that Sam (Yishan's friend) is also engaging in thinly-veiled bragging about these events.

Here is Yishan's comment with his name spelled out for clarity instead of just saying "CEO":

    In 2006, reddit was sold to Conde Nast. It was soon obvious to many that the sale had been premature, the site was unmanaged and under-resourced under the old-media giant who simply didn't understand it and could never realize its full potential, so the founders and their allies in Y-Combinator (where reddit had been born) hatched an audacious plan to re-extract reddit from the clutches of the 100-year-old media conglomerate.

    Together with Sam Altman, they recruited a young up-and-coming technology manager [named Yishan Wong] with social media credentials. Alexis, who was on the interview panel for the new reddit CEO, would reject all other candidates except this one. The manager was to insist as a condition of taking the job that Conde Nast would have to give up significant ownership of the company, first to employees by justifying the need for equity to be able to hire top talent, bringing in Silicon Valley insiders to help run the company. After continuing to grow the company, [Yishan Wong] would then further dilute Conde Nast's ownership by raising money from a syndicate of Silicon Valley investors led by Sam Altman, now the President of Y-Combinator itself, who in the process would take a seat on the board.

    Once this was done, [Yishan Wong] and his team would manufacture a series of otherwise-improbable leadership crises, forcing the new board to scramble to find a new CEO, allowing Altman to use his position on the board to advocate for the re-introduction of the old founders, installing them on the board and as CEO, thus returning the company to their control and relegating Conde Nast to a position as minority shareholder.

    JUST KIDDING. There's no way that could happen.

-- yishanwong

My understanding of what Sam meant by "I could never have predicted the part where you resigned on the spot" was that he was conveying respect for Yishan essentially out-playing Sam at the end (the two of them are friends) by distancing himself (Yishan) from the situation and any potential liability in order to leave Sam "holding the bag" of possible liability.