Did you read the article that the author linked to, in regards to this? You wouldn't walk up to a woman and say "You're a really great guy!" What would happen if you went into a mixed-gendered room and asked all the "guys" to stand up? If someone said "everyone knows it's a guys' world" what would they mean?

If you went into a restaurant with cutely-named bathrooms, and went into the "guys" bathroom, you would probably be surprised to find women in there. If someone described The Spice Girls as a "group of guys" that would likely be more confusing than someone describing The Beatles as a "group of guys"

It might sound completely normal to your ears to use "guys" in reference to any group of people because you're so used to responding to it (and, yes, I Internet-stalked you a bit to confirm your gender). Having never personally identified with the word "guy," however, I, at least sub-consciously, and sometimes consciously, think it's odd when someone calls me a "guy." I mean, I'll absolutely respond, and won't say anything to the speaker, but I'll feel a tiny bit put-off, and maybe a little self-conscious, because I'm the only person in my company who isn't actually a "guy"

Like the author also brought up, there are plenty of alternatives to "guys"