I’d say if that was unfolding in front of me I would not be moving much at all. :)
I know what you mean. Even though we see what appears to be the top of the cab of a truck in parts of the video, the cameraman (tourist!) doesn't seem to be that far away, that far up, or that well protected at all.
If those lions had decided to turn left towards the truck instead of right towards the buffalo, I suspect they could have closed the distance and jumped up into that vehicle before the driver could get it started and get them out of there. (I didn't hear any background engine noise in video, so I'm assuming the truck was turned off so as not to scare the animals.)
Ouch! Talk about seeing Nature in Action.
In that part of the world, humans are not at the top of the food chain. ;-)