Looks like he walked into the prop and as a result departed the scene faster than the camera could record it.
Not many airplanes used that V-770 engine and none were very successful. The XP-77, Edo scout floatplane, Curtiis Seamew, and the AT-21. A guy I know has installed a V-770 in his BF-108 and I was looking for info on it when I stumbled across that video.
By the time the AT-21 got into production its day already was over. I read not long ago that in 1943 they decided to standardize on the B-25 as the twin engined trainer and phased out the AT-9, Twin Beech, and similar trainers. They kept the B-25 as a trainer until the late 1950's.