I'd have to see it for myself to know what he was talking about. I doubt that the point of the video was about how transmissions and engines are blowing up all over the place because people are shifting them into neutral.
But still, the majority of (if not all) owner's manuals also recommend against shifting into neutral even with the engine on. In most places it's also illegal. The guy I knew that went over the edge of the pass also had his engine on. It's also more possible to shift into Reverse or Park while in motion if your average driver shifts into neutral all the time. And if you're braking anyway, there's no point in shifting into neutral and leaving the engine on at the same time since you'll use more fuel (and brake pads).
He could have been referring to any or all of these scenarios as being "bad."
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