Their chrome extension was hacked. Yep. Has nothing to do with hosting files on their website. Not really sure where you were going with this.

"You are only affected if you had the MEGA Chrome extension installed at the time of the incident, autoupdate enabled and you accepted the additional permission, or if you freshly installed version 3.39.4,"

Four hours after the breach occurred, Mega.nz uploaded a clean version (3.39.5) of the Chrome extension, which should have auto-updated affected installations.