I thought the fellow was merely trying to close the door as it wasn't shut properly so he opened it as you do to close it again and it must have blew open and he fell out.
So why did he wait until he was on the motorway to do it? Why not as soon as the alarm thingy went off (which presumably would have happened as soon as the car started moving)? And why wasn't he wearing a seatbelt?
As has already been said, he put many lives in danger, regardless of his reason for doing what he was doing. There could have easily been a multi-vehicle pile-up, and he's very lucky that the vehicle behind him wasn't a huge articulated lorry!