If I were to make a recommendation for this guy, I would tell him to do it all just the same, except for one thing: leave the last 10'-15' of branches on the tree, just below the top section that he cut off. Strip any branches on the side it was falling toward, so that it would not get hung up.
Top section falls, the trunk rocks left, then right, then stops at center. Easy.
Leaving a significant set of branches high up in the spar would act as a stabilizer for the oscillations of the trunk. They absorb energy by damping movement with their mass, and they add wind resistance to any movement. It would never have rocked back and forth so violently, and he would have been fine.