Humans think of hominoids as bipedal and hairless - the naked ape. Hominoid forms evolve naturally on many worlds, and just as the proto-hominoid on Earth was a hairy ape, the proto-hominoid elsewhere can take many forms. Due to the genetic engineering that takes place, grafting genetics from existing hominoid stock, the hominoid visitors that humans have encountered look similar to humans in the main, and thus have given the erroneous impression that this is the hominoid form. The naked ape is but one variation of the hominoid form. What is termed the Praying Mantis is a hominoid, and what many contactees take to be the insect forms of their visitors are almost invariably hominoid. There are alien hominoids that look like monkeys or apes to humans and a variation on this form is a furry hominoid humans take to be a bipedal cat.
Humans have whiskers, but not the stiff sensing kind that rodents and their pet cats and dogs possess, so seeing whiskers on the delicate face of a fuzzy visitor has caused them to assume these visitors to be cat people. Get used to it, Homo Sapiens, there are stranger hominoid forms yet!