It's just a common turn of phrase used by Incels. Not sure if you're oblivious to that, or just being defensive in the "not all men" vein of responses.

There isn't anything wrong with "females" as a term inherently, but it is a more clinical term and you find it a lot in really bad pick-up books. The choice of term is meant to dehumanize women (much in the way "girls" can often be used to diminish a woman's standing or accomplishments). It's not necessarily done intentionally, but it plays into a larger trend with the rest of his comment that this guy is pretty down the path to full blown incel.