That's fine if you're behind the vehicle right when it starts slowing down. I agree with you that a fatal accident is highly improbable there. But it didn't just slow down a bit and then resume speed. If you watched the video you saw that the vehicle came to a complete stop. The vehicles that saw it mildly slowing down have already driven by, leaving only incoming vehicles going 70mph unprepared for a vehicle ahead at a total standstill. Hopefully those unprepared drivers are sufficiently conscious, alert, and otherwise not distracted to react in time to prevent a crash. As the clips I posted above demonstrate, I wouldn't bet my or anyone else's life that that is the case.