I was kinda scared that they were serious in that Direct video for a second.....
Just to clarify, Beheeyem is based on extraterrestrial beings--there is a difference.
There are some of you that are a bit confused as to why Bigfoot is classified as a fairy and what the actual definition of a fairy is. When people think of fairies, they think of small and cute sprites with wings. People will think of Tinker Bell, Navi, and the like. However, these cute creatures are actually, by definition and lore, pixies. Pixies and fairies are similar, but have different origins are are not the same species; kinda like the difference between trolls and goblins.
Fairies, on the other hand, are beings capable of supernatural or metaphysical powers via magic that are said to form many legends and myths we know today. Fairies are of this world--which is what sets them apart from extraterrestrial beings--but not always of this dimension, plane, or time. Fairies are capable of spreading joy, causing mischief, or completely destroying nations depending on the type and morale of the fairy. Many fairies are incapable of flight or do not have wings. Despite many stereotypes, many fairies do not look humanoid at all (Slenderman and Big Foot).
Lets look at the reason Big Foot and Slenderman are classified as fairies. Big Foot is a creature that lives in dense forests from urban legend that none of proven to exist. There have been claims that people have seen them, but there isn't any evidence to back this. In many folktales (depending on the culture), Big Foot is able to preform metaphysical feats such as jump higher than most animals would be able to. These abilities while sounding simple match up to many of the abilities the lesser known fairy abilities (Oberon's slaves and servants come to mind).
Slenderman, on the other hand, is a maleficent being that does resemble a humanoid figure at times. It uses supernatural powers to change its form, steal children, aggressively stalk victims, and even mutilate bodies. Would you like to know who else is able to do the exact same thing? Oberon himself! Oberon is the KING of fairies and is said to be very maleficent in his own right. He has had mortal men rape his own wife just so he could steal his wife's slaves.