As has been quoted by others here, DI essentially had a US piggyback FAA 61.75 PPL no IR. This is normally gained for the purpose of holiday flying in the US or hour building there. According to airmen registry he also had an FAA Class 2 medical. Whether or not an FAA Commercial was pending update online, and was he flying with a FAA CPL temporary airmen certificate ? has not been addressed, my guess would be that he probably only held a 61.75 PPL and his UK licence. Therefore no requirement for FAA written exams for the issue of an FAA PPL and therefore it’s possible there was little to no knowledge of FAA regulations.