It's not incorrect.
From Merriam-Webster:
3
a : man, fellow
b : person used in plural to refer to the members of a group regardless of sex <saw her and the rest of the guys>
Or perhaps you prefer Oxford:
noun
1 informal A man:
hes a nice guy
...
1.1 (guys) People of either sex:
you guys want some coffee?
Sorry for off-topic, but I'm not a fan of people trying to dictate what language is "correct" to use in a non-technical setting, especially in this context where both of the most well-known/respected dictionaries agree with the asexual usage. Also, sorry, but it's a man's world

Do what you want, I'm not stopping you. I'm just trying to make aware its cognitive effects.
Dictionaries tend to record popular usage (where did popularism ever leave governed society?) of language but etymologically, a guy is still a man, making guys to refer to anything other than a group of men, etymologically incorrect despite a social norm. You don't refer to a female as a guy. A guy definitively represents a male.
If you're interested in the controversies, subtleties, and implications of continuing this defect of culture, it's a career-long topic of
Prof. Hof that he can give rhetoric, general and specific anecdotes, and just enjoyable conversation about, for every reason that I agree. In summary, it propagates a subtle male supremacy of society in a world where women are continually harassed by social norms.
Don't get me wrong, I still slip "guys" incorrectly at times, but I always catch and correct myself now that I know better.