I have regular sports massage and they thought it was a tight glute medius. Watching your video again and doing other research i think it's possibly a weak glute medius
I think a muscle shortens by pulling the muscle from the insertion point and to the origin of that muscle. Michael kind of confuses this concept by saying that both the origin and insertion point pull in order to shorten a muscle? Please correct me if i'm wrong.
The muscle contracts, and so the origin and insertion will come together. Whether one moves more than the other depends on whether the joint is being held in place by any other muscle or bone structure - for example, when the pectorals contract you can't really expect the origin at the sternum to move, so the insertion at the top of the humerus must be the part that moves.