Earlier quoted context omitted.
Third possibility is Twitter's anti-abuse flagged a suspicious login and locked the account for your own protection. An instant, algorithmic ban limits the damage the impostor can do.
Author should have received a warning email about it, unless it's compromised as well.
One to indicate that my account was locked (2 minutes after that particular tweet was made), one that my appeal has been logged and one that I tried to log in from a machine that had not been seen by Twitter before (true, a VM temporarily booted to check whether or not the password had been changed).