Well the thing about 90 minutes is definitely a red herring, the check-in cutoff for domestic flights is 45 minutes and if he got to the gate then surely he checked in successfully somewhere whether online or at the airport.
AC denied boarding for some reason. Maybe overbooking, maybe they closed the flight before resolving whatever the issue was with his ID (???) in order to get it out on time, maybe they cleared a standby passenger into his seat. Assuming he presented himself for check-in and boarding prior to the respective cutoff times with valid ID, it seems to me that AC should compensate him.
The thing about his girlfriend is just... weird. But not really material to the situation.