Sometimes human Earth people pretend to be aliens in order to fool other human Earth people. But in actuality, few to no aliens were involved in their scheme. They do this for many reasons, ranging from April Fool's Prank and gaslighting to date rape and government conspiracy. People who want to pretend to be aliens are actually more creepy than actual aliens, because at least aliens are honest about it (or would be if they weren't so damn mysterious!)
Extra-terrestrials find this sort of appropriative behaviour extremeley offensive and so does every one else.