That's what the article said "A witness on the scene said it looked like there were two separate collisions, with the second one caused by the drivers trying to avoid the first. "
Good point, I still can't believe Tesla's AEB will only reduce the speed by 25mph instead of bringing the vehicle to a stop or near stop. That system seems so antiquated. At this price range you'd expect something up to date, even class leading, but Tesla's current AEB is neither of those and should be updated ASAP.