I just went back and re-watched that scene, and Don and Joan are sitting at the bar, and then the bar makes a right angle and the guy is sitting a little ways down on that other side that's perpendicular to them. If they're facing forward in their chairs, that guy is at about 10 or 11 o'clock, not 7:30. Maybe you're thinking of a different system of describing position by the numbers on a clock. The one I'm familiar with is 12 o'clock is straight in front of you, 6 o'clock is straight behind you. 9 o'clock is directly to your left, 3 o'clock is directly to your right. So 7:30 would be behind you to your left. That's not where the guy was sitting.