My theory, based on the fact that he had a shopping bag, was that the dude in the tank was his son:

"Hey, didn't I tell you grandma and grandpa are coming over tonight?"

"Uh, yeah dad, could we talk about this later?"

"No. And do you remember how I specifically asked you to pick up some lettuce and tomatoes on the way to work?"

"Uh, dad, we're kind of holding up traffic here... WHAT THE HELL, DAD PLEASE GET OFF THE TANK, PLEASE, YOU'RE EMBARASSING ME"

Tank Man was later given a medal for Most Epic Dad Moment

Aww, that would be so romantic

Guy buying groceries seeks Lt. tank commander for romantic candlelit dinner to discuss merits of Deng's reforms in light of the student protest movement