It’s easier to understand NAND retention with relation to temperature if you consider the following:
1. Think of temperature as a measure of kinetic energy (vibrations) in the constituent particles of a system (NAND).
2. NAND is like an array of capacitors (containers that hold electrons) that store electrons. 0 or 1 depends on if electrons are present.
With that in mind, vibrating particles (electrons) are more likely to escape their “container” as they they vibrate harder (increased temperature); this is bad for retention. This also makes them easier to erase however (good for writes, less stress on the “container”).
This is very simplified obviously, and off the top of my head; the concept should be sound however.