I think it's like everything else we discuss here: less rare in our kids than the population at large, and probably getting less rare all the time in the population at large. Early puzzle ability probably will be seen more in visual-spatial learners, but I'm certainly no expert.
I think that aside from how rare your kid is in their experience at that preschool, though, having a maximum of 8-piece puzzles in a room for preschoolers falls in the category of severe dumbing-down. I'd carefully evaluate everything else he will be exposed to, but it sounds like you've got them listening already, which is good.
