If input is not what was expected but is handled correctly is it valid?

I'm doing software testing on a web service and I'm wondering, if the web service takes a zip code and returns coordinates of the zip code. if I input 99999, which is not a zip code, but the system doesn't crash, it just replies with a 0 on both coordinates, is that considered to be an invalid input? I'm not really sure since it is not crashing the system, it means it can handle the input, so does it make the input valid or is it still invalid due that 99999 is not a zip code?