In current usage, people almost exclusively use "alien" to refer to ETs. The only ones who use it in the sense of "foreigner" are immigration bureaus, and this becomes a source of hilarity whenever they speak to the outside world.

Would you ever say "I had some aliens in my home last night for dinner" and expect someone to interpret that to mean immigrants/tourists/strangers? At best, they would criticize you for using that term to refer to them.