That a mild slowing of the vehicle ahead would cause a fatal collision that wouldn't have happened otherwise, yeah.
This called for the same reaction as would adjusting speed to match any car that took their foot off the accelerator; the Jeep didn't even brake! Driving is a continual process of these slow interactions and that's not the part that causes accidents, and considering relative speed they would also tend to be non-fatal accidents if they did happen.
That just makes it more dangerous - there was no brake light to clearly indicate the car was slowing. Since we know drivers rear-end cars quite often we know the risk of accident was increased here.
Increasing the risk of accident is not acceptable unless all participants have given informed consent (they didn't).
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.
A fatal collision can kill more than one person. Also, more than one car was impacted by the slowdown so you need to look at the overall odds per person not per car and then sum then to find the collective risk of death.
It's not easy to find the actual odds, but stopped cars on the freeway kill people every year with much higher risks in high speed low density high speed traffic as traffic jams tend to be safe it's unexpected stopped cars that's the problem.
Rough guess there is probably a 1:100 chance per year a car will stop in the middle of a free way for no apparent reason. There ~100,000,000 cars on the road. So, ~1:1,000,000 cars stop per year which is probably low but let's say they cause 10 deaths out of the 20,000+ auto deaths per year. Well that's ~1:10,000. Now, sure you
can play with the odds but there much higher than 1:1,000,000.
This called for the same reaction as would adjusting speed to match any car that took their foot off the accelerator; the Jeep didn't even brake! Driving is a continual process of these slow interactions and that's not the part that causes accidents, and considering relative speed they would also tend to be non-fatal accidents if they did happen.