He doesn't qualify for a visa, because a part 61 cpl doesn't require a full time course of study for the duration of his visit. (That would be: 8 CFR 214.2(f)(6) and 214.2(m)(9))
Where do USCIS say flight training isn't vocational? The M-1 Visa is for vocational training! Why does noone have any source for these 'new rules'. I've yet to see anything which indicates a visa is required.