Two things from the updated article:
1. "Cruise employees performed an "extensive" search of the ship, but the spokesperson said the 26-year-old wasn't found."
2. "McGrath wasn't detected by the ship's surveillance systems and wasn't seen by U.S. Customs and Border Patrol during the cruise's debarkation process."
So that theoretically leaves out 'stowaway', and it also leaves out 'he ditched his family and completed the CBP disembarkation process normally'.
According to this
Business Insider article, the last person to see him was his BROTHER, and that's the cabin mate referred to. This article also says the
last sighting was at 2am (by the brother), and that he was
reported missing at 7am. The Fox article says the last sighting was at 7am, so we have some conflicting info.
Coast Guard is searching the area.
I'm kind of surprised CBP & Miami police cleared the ship to depart again, but the almighty dollar and all that.