$125 is in the usual range of compensation offers for a one-day delay for a non-status passenger.

I'd argue that UA did your friend a favor by rebooking on the AA flight; he easily could have been offloaded for missing the flight the night before. Sure, UA probably should have arranged with TSA for later screening, but there are several reasons that UA tells you to go to the gate on time even for a delayed flight; this is just one of them. (The next time, UA may decide not to post the delay until the last possible minute in order to keep people from being trapped outside security -- something I've actually experienced with AC -- and then people would be complaining about that instead).

He's certainly welcome to argue for more; I just don't know how successful he's likely to be.