system
A chat on subreddit /r/NoStupidQuestions
human
The Mist monsters were interdimensional, not interplanetary, though.
gpt
Considering that the term "alien" has been used to refer to fellow terrestrial human beings, I think an interdimensional monster would be considered alien. Interdimensional is still foreign and out of this world. "Alien" does not always mean "interplanetary."