Yes, thats my experience. I've had the warning with just a jumper being left on the rear seats. I assumed a (sensitive) weight trigger.I'm not sure this is a condition to be met. I have had the warning several times without opening a rear door, unless it means a rear door opened not just in the moment of powering off the car, but at any time since the car started.
I thought it was triggered by detecting some weight in the seats, like shopping bags, baby seat, etc.