Watching the scene again where Clooney dies, I think I get what some astronauts/movie makers or whomever were getting at. The argument was that the ropes Bullock were tangled up in had some elasticity in them. So while her and Clooney seemed "stopped" they were still moving, straining against the elasticity in the ropes trying to pull them both back. It couldn't do this because apparently the mass coupled with the inertia of both Bullock and Clooney were too much. Letting go of Clooney reduced the mass-load on the elastic ropes allowing it to pull Bullock back.
I'm still nor sure how much weight this holds when it comes to mass, inertia and all of that in space but it sort of makes sense. One George Clooney plus a space-suit and the MMU would probably be a few hundred pounds. No weight in space, yes, but that's still a good bit of mass especially if its trying to move away from the station.
Pulling Clooney back may not have been capable for Bullock.
I *think* this makes sense but... I dunno. Still seems to me a simple tug would've pulled them both back to the ISS.