Watch the video again; the little red car turns on their blinker and does a very slow shift to the right before clipping that stopped SUV. You're right that he wasn't paying attention, but his reaction time is incredibly slow - it looks like that car had just enough time to slam on their brakes or swerve to the right, yet they did neither.
aren't you supposed to have a wide enough space between you and the car in front of you? to compensate for any slowness in reaction.
I think the situation is not entirely unclear, it seemed that there was a problem ahead of the SUV, that made a bunch of cars slow down altogether. I still don't understand the smaller red car driver decisions.. maybe he didn't know what to do and hesitated and tried to swerve as a last resort. Or maybe he was just not watching. The SUV break lights were on quite a long time..