Being a Cowboys fan, I was watching that when it happened. Pretty funny.
Because it had been a touchback, Romo knew if the ball wasn't spotted touching the 30 yard line, it would not be a first down, so he was just messing around and giving it a little nudge to help out. They probably could have flagged him like Allen (69) wanted them to, but they didn't because Romo was just joking around and it's not like he tried to hide it.