I saw someone assert the other day that one’s wrists do not and cannot get bigger from weightlifting.

This is wrong; they do get bigger. Since I started lifting heavily again, mine are about half an inch greater in circumference. This is because as you lift, your bones, tendons and the muscles in your wrist all get larger.

My wrists are naturally pretty thin but I am sure it is true that their size will increase in everyone, given enough lifting.