He didn't own the name, he found a way to change the DNS records; while being registered at MM, google.com is still pointed to Google's own DNS servers.
They're a reseller like everyone else. If I'm not mistaken they actually use eNom for customers buying domains on any of their platforms (though not for their own domains).
I get emails for a friend's domain that was originally registered through Google Apps (G Suite) many years ago, and I see emails with "enom" in them going back all those years.
Domain Name: GOOGLE.COM
abusecomplaints@markmonitor.com