Is it possible for rain to enter the cabin of a car and not get anything wet except the right rear passenger seat floor? And I don’t mean damp, I mean standing water in the floor.
Sure, if the weather stripping around the door was leaking in the right place(s). It could trickle down the sides and seep out of the bottom, collecting in the footwell.
No, it’s impossible. You’re imagining it. There is no standing water in the rear of your Altima.
Seriously, a clogged sunroof drain might do this. So could a leaking back window, a bad rear door seal, a rear door with clogged drain holes, or a window left open.