I was really, really bored this morning and intrigued by this issue...so I Googled 'nissan seat reclines by itself' and saw many similar complaints with other Nissan models...like Armadas, Titans, Pathfinders, etc. Some as far back as 10 years ago. There were also similar complaints for other makes.
I looked at a few threads and saw no definite smoking gun causes. But a popular hypothesis was that if the driver was overweight they could unknowingly hit the buttons as they slid out of the seat...due to the proximity of the buttons to the edge of the seat. Another popular thought was that taller vehicles caused the driver to have to slide off the seat and down to get out...causing them to mistakenly hit the buttons. I read of only a couple of people who claimed to had actually seen the seat move without physically being in the vehicle.
The one thing that I saw that all the complaints had in common were that they were all mostly taller vehicles.