Whatever the initial cause the aircraft's angular momentum was soon greater than the machine control and/or pilot's ability to counteract.
Well.... yes.... eventually during the event, but.... The tricycle is naturally directionally stable on the runway (unlike a taildragger, which would surly behave this way once initiated). Once the destabilizing force was removed (asymmetry reverse, I opine), the plane would have naturally aligned itself to it's path (the runway centerline hopefully). But, yes, you can get to a point where that won't work anymore, and this pilot did.
This would be similar to landing with a flat tire, controllable, but you have to!