Not saying he isn’t using the force to make his cape billow, but he’s definitely not in a vacuum
Both ships have air in them. They probably are not running at the exact same pressure value. It is totally reasonable that there’d be enough air flow just after exposing each other to the varying pressures.
but the air would be leaving the ship, blowing his cape in front of him, not behind
You are using real logic, you need to use fantasy space retcon logic.
On open space ports, ships suck the atmosphere back in to not lose air using a gravity generator, which would cause the cape to blow towards the ship. Expect this to be a small plot point in “The Mandolorian and Grogu.”
It’s like force choking somebody if you stand directly in front of him. Such a poser.
How do you think they breathe if there’s no air?