Down under here is Aus. Guy means Man. Guys means ppl. There is no discussion on this point.
It's sort of like in Spanish, where you have Pera and Pero, for Bitch and dog, but unless every dog in the pack is a bitch, you call them Peros, whether their all male or mixed.
I believe this applies to any number of nowns in most European languages. It's rare to see it in English,but it's a language of exceptions. ;-)
In reality it's simply highlighting the chauvinistic nature of all languages, but it's hardly worth getting upset about, as CG points out.