>>32420561TECHNICALLY Grass-type is representative of the ancient chinese elements, of which there was """grass""" (low-lying vegetation) and also """wood""" (trees etc) Gamefreak combined the two into one type, but along with that (and with their culture arguably) came the association the mushrooms are just like moss or grass or flowers. To them, it makes perfect sense. Plus, most people don't even know mushrooms aren't plants. You overestimate the average intelligence of people.