i have a theory that the term alien and extraterrestrial were intentionally conflated by the air force as a coverup for the roswell witnesses seeing captured asian pows being used for radiation exposure experiments. they saw the battered and emaciated corpses of jap/chinese/korean test dummies, and the government freaked out that the public would rightfully object to this on humanitarian grounds. they also saw the documents describing these human guinea pigs as "aliens" which was the official term for someone in the usa who wasn't a citizen. so when somebody said "it looked like extraterrestrials", it was a super convenient way to explain all this unit 731-tier nightmare stuff away, and the brass rolled with it.
Canada