Re: Real Twitter news...
Musk was talking about sign-ups, not readers. He was not saying lots of new people followed a link and looked at a page of tweets. For a sign-up, a human or bot came up with a unique user name and something resembling a password then jumped through whatever hoops are required to prove/pretend they are not a bot.
Your reason for them doing so is that end to end encryption has been mentioned but is not yet implemented. Even before I start thinking, that seems fr fetched but lets follow this through. Plenty of people click the 'track my every move and sell my data to anyone who offers a little money' button because it is only one click instead of often two plus a little reading and thinking. None of that crowd are going to make the effort to sign up for your reason. Next up, there are some whose lives depend on their communications remaining private. They will make a proper effort to research the product. With the minimal possible effort they will find "not implemented yet" and move on.
Perhaps one day Musk will say encryption is working. On that day anyone with a clue will find out who provided a billion or more to help Musk buy twitter. That list of names would scare away anyone with a genuine need for private communications.
I prefer some other theories.
1) Musk simply made it up. People have a bad habit of believing what they are told despite evidence to the contrary and doing what they think others are doing. Just by saying people are signing up in droves Musk will convince a bunch of people to sign up.
2) One of Musk's employees made it up to avoid getting fired.
3) Some bot herders are taking the opportunity to create a pile of new accounts while Twitter is too short staffed to stop them.
4) Musk hired some bot herders to create accounts that follow him and like his tweets.
I would believe any of those and a bunch less likely over people making an effort to get encryption that is not yet available.