Those things have a high and low speed switch which he obviously didn't know about the slow speed. He could have eased if off the slab with no problem. His first experience with the front falling should have given the idiot at least a clue as to what would happen when the back came off with opposite reaction from the front, but in his stupid mind it didn't register. Another thing he could have done was operate it from the ground station although I am not sure that the travel option is available. I know all the boom functions are though. OSHA rules that you must have a safety harness when using those machines also. He would still have been banged up a bit from his stupid act, but the fall would have arrested after only a little less than 6 foot rise (most lanyards are 6 feet long) at which point he would have been whipped back downward, likely banging off the basket a few times. He may have survived with fewer injuries without the safety harness in this case.
I once saw a guy run one of those off into a ditch on one side with over 90 feet of boom out. He was harnessed in but the boom fell across a pipe rack putting a 45 degree bend in it, tossing him out at which point he was hanging in the air about 40-50 feet off the ground. He had some lacerations and bruising but he would surely died if he had been thrown out without the harness.