I think this might be a disconnect between what those lights are "really" for, and how they're actually used (de jure vs de facto, in a sense).
They aren't meant to have a specific meaning, they're just headlights, but when going in reverse. So if the car has a feature to "turn on the headights" it makes sense to activate the ones on the back too.
Though that's just pedantry that kicks the can down the road to the question, why are the headlights turning on with nobody in the car?
The specific use is to light the way when reversing. They are not intended for use as "reverse" indicators, even if that's what they're used for in practice. Trailers usually don't have reverse lights, for example.
Yeah, you could have a whole article-length rant about how courtesy lighting has devolved into turning parked cars into simulations of a rocket launch site lit with flood lights.
The dwell time on these modes is so long that you need a welding mask to protect your eyes if you make the mistake of waiting in a supermarket parking lot for someone who is running a quick errand. Just a constant stream of large, unattended SUVs blasting ridiculous light into surrounding cars. By the time one turns itself off, the next one is ready for duty.
They aren't meant to have a specific meaning, they're just headlights, but when going in reverse. So if the car has a feature to "turn on the headights" it makes sense to activate the ones on the back too.
Though that's just pedantry that kicks the can down the road to the question, why are the headlights turning on with nobody in the car?