No, no, not that simple. Chain coming off doesn't ALWAYS lock up the rear immediately. So chain comes off, bike is still rolling, he waves, starts to brake. You can see this in the video. The chain is off first, then the brake light comes on. THEN a second later the chain gets caught, locks up. After the bike takes a tumble and the wheel isn't turning forward any more, the chain comes loose again. It's possible and I'm willing to give him credit for that being the scenario. Otherwise there is nothing about the chain being off that would motivate someone to lock up the rear brake. The wave (for whatever reason) which came after the chain was already off, indicates that he was hardly in a panic.