Wonder how they calculated the "average" temperature. Was it weighted by mass or by volume?

That's purely academic. IRL what actually matters is “how big and reflective is the thing you're in”.

You'd get real hot real fast in a matte black space suit.

Well yes, because space is not actually a complete vacuum.

Cold is the absence of heat in a medium that can interact with temperature imo. It certainly wouldn't act like normal cold; if you stuck your hand out and felt the vaccuum, it wouldn't feel cold, and the heat in your hand would not flow outwards into space very much. There's no convection, only radiation. Space isn't cold, matter is cold, and there's no matter.