What does he do with it? The page you get is a simple 'x' only.

I am hoping he has loads of stuff on hidden urls, and uses it for personal email or something. If he's just sitting on it doing nothing, then that's just plain wrong.

x.com/musk has a y Or any /<something> results in a y

X.com was registered in 1993 but bought by Musk in 1999. He lost the domain name by leaving the Paypal but bought back the domain name from Paypal in 2017: https://twitter.com/elonmusk/status/884580654117076992

X.com is one of the few single-character domain names that created before IANA’s restriction of single-letter and single-digit domain names registration in December 1993.