Twitter is private, there’s no public shares anymore. The number you found was his stake before he purchased all the shares and before Twitter was taken off the markets.

Yes you need to have 50%+1 share to have complete control over a company.

Twitter probably still has shareholders, but that’s between Musk and them. Think about Shark Tank, when they say “I’ll offer X$ in exchange for Y% of the company.” Well Musk had to get the money to buy Twitter from somewhere.