Many Nissan vehicles, the Z included, will roll the passenger windows down if the "unlock" tab on the fob it depressed for a few seconds (probably 5-10) and if you keep holding the tab, the windows will roll completely down (my M45 does the same with all four side windows).
That's likely what happened here.
Also, some of you may not realize that you can put all windows up by using the key in the door lock; turn the key to the lock position for a few seconds and hold it there and the windows will roll up...convenient if you want to roll up your windows without messing with the ignition/starting the vehicle.
