We have that same rule about leaving our work laptop in a car unattended. I've followed that rule pretty religiously, so if I go to the grocery store on my way home, I do my grocery shopping with my laptop bag strapped to my back. But even I've violated that rule at least once when I've left my laptop in the car while I sprint to get my lunch that I forgot in the fridge.

And even though the security risk from the laptop being unattended in the car for less than 60 seconds is a violation, if someone was so determined to get my laptop within that kind of a timespan, they'd be determined enough to grab it off of me in person. So the practical security risk there is zero, but you could still grill my ass for it.