It's doubtful the scrape rate was that high all of a sudden. However Musk needs money. And excuses to get them.
Scraping is perfectly legal.
The lawsuit also sues for "taxing/degrading user experience" so they're trying to not position it as "they scraped us".
Once he knows who it is, he'll probably try to pressure them more based on the product they've made with the tweets. If any.
He's paranoid everyone is stealing his tweets and making super-profitable AIs with them.
It's doubtful the scrape rate was that high all of a sudden. However Musk needs money. And excuses to get them.