Draw on your own experience. If the wind causes your jacket to billow, (not agreeing this is what actually happened to The Cuban/DCM), you grab the left and right sides of the jacket, pull it forward, and then zip it up. Same goes for a soldier when straightening his uniform jacket/coat gripping the Sides and pulling Down in order to remove any wrinkles. He does Not reach Back/Behind himself.
You're describing a heavier-weight coat. Guess they don't sell windbreakers where you're from.
Reaching Behind yourself and Down into the butt cheek/back pocket area does Not occur when attempting to straighten/zip up a jacket. This is Not we are seeing The Cuban doing.
If he's not taking in his windblown jacket, then how does the hands resting on the outside surface of the cheeks mean he's tucking something
INTO his pocket or waistband, or up his back?