Just to check all things here…

“Expired” is a strange word to use unless referring to a ticket that had passed its one year validity. This was a brand new ticket being purchased, not using a travel credit voucher or revalidating a previous ticket, right?

In any case, I can’t understand how he would have gotten through check-in, TSA screening and as far as the gate with what sounds like a perfectly valid boarding pass if there was anything wrong in the ticketing. Shouldn’t have happened.

Finally, there wasn’t anything else that might have been expired, was there? Driver Licence or Global Entry card or whatever he was using to travel? This should have been caught at check-in or TSA, but I can imagine that it could happen sometimes.

Finally, sorry to hear of it. Sounds like a real pain.