Why would Jh go to breakfast if he was running late.
My husband can back up better than me, and tries really hard to teach me to trust my mirrors and he rarely would look behind if he was backing into a parking space. Thankfully I have a back up camera now, I won't tell ya all how many bikes I have run over, kid free of course.
I think JH didn't have to look behind when he backed up. But try sitting down in a chair. And think of the height difference or the car seat and JH head, the motion you might turn to grab a coffee, or maybe a bag. You would see something in the corner of you eyes, and even without moving, you could see the small portion of the car seat. Backing into the space you would look into mirrors, moving your head and you'll see the car seat in the corner of your eyes. I think he would of remember at that moment, oops still need to drop Cooper off. But he didn't drop Cooper off.
If he was in late, maybe in a rush, why take the time to back into a space.