totally under-educated guess is that the rear door was open, co-pilot went to look at the landing gear but didn't/forgot to strap into the safety line system the jump-master was using (in the video) and they hit some turbulence that put him off-balance or off his feet completely and out he went. regardless, rip.
Depends. Where exactly in space is the shuttle when you push away? You could go left, right, up, down, or nowhere, depending. However, in many of those scenarios, unless you're in a space walk suit, you will be dead, and it will be your lifeless body (or its exploded parts) that goes or not.