IANAL, but if the boarding pass says T-10, that should apply rather than the T-30 that *we* *know* applies to international flights. Of course, it would be better if the passenger had proof of being at the gate by T-30.

Since this was an AA flight from the EU (currently) to the USA, the passenger has a choice between claiming under the EC261 regulations or USA DOT rules (which require an IDB to be a situation in which the flight was oversold, so the OP should try to find whether the flight departed with empty seats and whether nonrevs/standbys were boarded in the end).