I don't think the older equipment was the problem. The mismatched RF deck/transmitter could very well be a problem. Just the fact that he is now suspect is one very good reason for NOT skirting the law . YES the mismatched setup could cause problems . The very setting that makes for "narrow band" transmission is the deviation level. Too much drive to the RF deck could cause off channel harmonics.
Also the RC license is no longer required on the 72 MHz band .
That is an out of date regulation. The type acceptance is gone as soon as the HiTec module is plugged in to the other brand TX and turned on.
May be hard to collect ,if I were him I would pay up just out of embarrassment
It is nice to be operating within the law when someone has a plane trashed from interference.