It seem the pilot lost control of the plkane. The fact is knowing what he was doing that time. I read several books of WW2 pilots who say that the P-39, due to the location of the engine, was not at all a plane to be used for aerobatic.
A number of Italian pilots, flying P-39 with co-belligerant Air Force (ICAF) in 1943-45, run into accidents and even died just because they were doing aerobatcs with their Aircobra.