Are people really that dumb to think that there are only U.S. citizens and illegals?

Yesterday this person asked me if I was a U.S. citizen and I told them no I have a Green Card. So he was like "are you illegal then?" Why are people so dumb to think that you if you're not a U.S. citizen then you must be illegal? Do they ume that the word immigrant and illegal are synonymous? duh!