We'll have to wait for any official report but an engine failed causing the window to fail because of flying debris at lowish level, which means the differential pressure (inside v outside) was probably relatively low..
From unofficial early accounts it sounds like he then ended up with the airflow jamming his head against the open window frame, but he was restrained mainly by the seatbelt.
Obviously very nasty but possibly not quite in the league of some previous incidents/accidents, and sounds like all the crew did a good job..