It seems like a common misunderstanding because the reporting around this is so bad.
> Musk and Twitter agreed to a so-called reverse termination fee of $1 billion when the two sides reached a deal last month. Still, the breakup fee isn’t an option payment that allows Musk to bail without consequence.
> A reverse breakup fee paid from a buyer to a target applies when there is an outside reason a deal can’t close, such as regulatory intermediation or third-party financing concerns. A buyer can also walk if there’s fraud, assuming the discovery of incorrect information has a so-called “material adverse effect.” A market dip, like the current sell-off that has caused Twitter to lose more than $9 billion in market cap, wouldn’t count as a valid reason for Musk to cut loose — breakup fee or no breakup fee — according to a senior M&A lawyer familiar with the matter.
He is obligated to close the deal and Twitter can force him to do so. If some external force stops the deal from happening - or if he can show that Twitter egregiously violated the agreement - he can get away with not buying Twitter, but he still has to pay them $1B.
The point is that paying the ‘fine’ doesn’t give him the right to walk away for ‘no reason’. If he does he may end paying damages for much more than $1bn.
So he's using the 'bot' issue to find an excuse for a deal he wants out of.
[1] https://www.cbc.ca/news/business/elon-musk-twitter-1.6432315