I'm leaning more towards stolen ('borrowed'?) and real gear. In some of the video it can appear at times that he even has a headlamp attached. I figure if he has access to the gear at all (without purchasing it), he has access to ALL the gear. The complete outfit.
I agree that he didn't look entirely comfortable in the gear...that he wasn't someone who was accustomed to wearing it. Agree, too, that he had several tools attached to it (that, and some of the screenshots, make me think it could be real gear).
I am undecided on if the boots were too large, though if borrowed and part of someone else's SWAT uniform they might be, at least slightly. I think this is a guy, and at 5'7" to 5'9" range that makes him shorter than average, with likely smaller than average feet. In the clip at the end (after coming out of room 12) where he is standing still, his feet and boots do not look excessively large or floppy to me, and I'm inclined to believe a still shot over a moving freeze frame, which can be blurry. In any case, if I were going to commit a murder, and anticipated running or struggling on my feet, I'd make sure I could at least manage to do that in my chosen footgear.