It may well be that he was targeted because of who he is but I would have thought it's the sort of profiling that would routinely happen at the border.
Single male, last minute trip, driving an expensive car that isn't his would all justify further questioning.
Not declaring the cash is an offence, and would certainly justify further investigation including looking for intelligence such as phone records.
Only surprise in this day and age that you still need someone's pin to read/download contacts and messages.