I think the market valuation decrease due to the drop in the stock market overall is the real reason behind him pulling out of the deal as it was.
That said, I do agree that he has a valid argument about the bot problem on Twitter.
However, no one is talking about the real problem Twitter is facing.
Twitter claimed only 5% of their accounts were bots in official SEC filings. As a public company, that information must be valid and accurate.
If Twitter was to find/prove that it was more than 5%, especially a lot more, then the SEC would likely investigate the company and all Twitter shareholders could conceivably file a class-action lawsuit against the company for misrepresenting their public disclosure details.
In other words, Twitter has a lot of incentive to never confirm or admit that more than 5% of their user accounts are bots.
The best strategy for Twitter's board would be to negotiate a lower purchase price with Elon Musk under the premise of the "major market downturn" being the justification.
If this does go to court, Elon Musk's lawyers will inevitably subpoena the data Twitter refused to provide. That could create a lot of financial headaches for Twitter, including SEC investigations and fines as well as shareholder lawsuits, even if they win a settlement from Musk beyond the $1 billion agreed to exit fee.