Ok, if I was the director for this movie

and was trying to justify Mr. Wick's one handed press check, I would argue that in all the excitement of the moment he was just making absolutely sure that a round dropped into the chamber. It could be because he can't hear anymore firing so many rounds in an enclosed space or he's paying more attention to his environment and didn't notice the round going in, so he does a press check to be sure.
I can definitely 'feel' the difference between a round going in and a slide dropping on and empty chamber but if you're surrounded by super assasins hell-bent on killing you then maybe you don't notice these things during a reload, so a press check is in order.
So one handed or two handed? In all your excitement, using two hands, you may just rack the slide too far back causing a feed jam or you might eject the loaded round, altogether. Using a one handed press check, you're less likely to do that.
Ok, that's the crap I would feed the actor but my real goal would be cinematic flash! Getting one of those, oh so popular, movie moments that's gonna have audiences everywhere saying, "Oh $h!t, did you see that? That was Bad Azz!"
Translation $$$$$ since my career as a Hollywood director is now assured.
Anyway, just my random thoughts on the issue.

When it hurts – observe. Life is trying to teach you something... Your pain is the breaking of the shell that encloses your understanding.