PB - I'm not buying that, I sell and install dash cameras. Even with a 128 gig card with normal recording on a decent camera you're going to have about a 6 hour loop. Unless triggered to save by motion or impact "event" the recording will just keep looping. Wasn't this on Sunday or Monday? Unless the driver got home, pulled the SD card and sat on it for a day or 2 the dash cam probably would have just looped over that footage.
Plus it does not appear any driver's hit their brakes? Naturally seeing something like this to your left you would brake at least just to see what the hell was going on, and there would be a little bottle necking IMO.