Also the muscles in your wrist often go between, under, over bones, so your bones may "feel" hard on the outside, but that doesen't mean you aren't experiencing hypertrophy below/inside that plane.
The flexor digitorum superficialis flexor carpi radialis, flexor pollicis longus, palmaris longus, etc....all capable of growing and getting stronger.
Ever looked at the difference in size between the wrists/hands of a butcher?