Your understanding of those terms doesn't guarantee that the people describing the Xindi as insectoid or primate are using the terms literally.
The fact remains that the different species of Xindi have differences in their anatomy and biology that are just too far different for them to be closely related. We see no closely related species on Earth that are so wildly different. As I said before, it would be impossible for the different species of Xindi to be closely related unless evolution worked in a very different way on Xindus. And, as I also said, that is practically impossible.