Apparently Mr. Mavromatis owned a consulting company named Aegean, and it was his boat. It sounds like he rented (chartered) it out (to others) when he was not using it, so maybe that's where the idea started that it was a rental boat (which I also read in earlier accounts).

http://www.examiner.com/article/4-dead-newport-ensenada-race-including-aegean-s-theo-mavromatis

From the linked article:

Satellite guru Theo Mavronmatis, President and CEO of Aegean Consulting, Inc., specializing in the telecommunications and aerospace industry, was racing the Hunter 37, Aegean. Reports have Mavronmatis winning the race in the past. He rents Aegean out at Marina Sailing. when not using it.