The funny thing is that he didn't simply order his artist to create the scariest possible monster. He told the artist to start with existing skeletal bones and skulls and reconstruct one of them using the assumption that what he was dealing with was a bipedal ape with huge eyes for nocturnal hunting which corresponded to the huge Neanderthal eye sockets, the 8" fur coat which all ice-age creatures had to have, and maybe a slightly mean look on his face. The fact that what actually emerged looks as scary as it does is probably, as Vendramini suggests, an instinctive reaction on our part from racial memories having to do with having to deal with the creatures.
BTW, I thought gorillas were omnivores. If they don't eat meat, what do they eat? Can they get that big just eating plants and fruit?