>>46827528this doesn't explain sandshrew being the mouse pokemon lol
also, the word "鼠" specifically refers to muroids, a superfamily of rodents that includes mice, rats, voles, and others like them
porcupines, however, are part of the suborder hystricomorpha, which is separate from the suborder myomorpha (where muroids are found)
tl;dr all rats are rodents but not all rodents are rats