FYI: In my 2009 VW Tiguan, you don't have to slide the cover shut to turn off the light. The light will also go off when the visor moves back up.

So I can easily believe – and in fact now think it's the most likely explanation – that the renter slid the cover open and the light didn't come on. Without the light on, there's no reason to even think the slider should be closed. Someone unfamiliar with this mechanism might not even realize that when everything is working, the slider works as an on/off switch.