I have so much fun joking with some of my women friends that they're sexist because they're using "guys" instead of "folks".
To me, it's one of those things where someone is always going to be awkward and say "that doesn't include me". They may jokingly say something but some take it as a personal insult and just assume the other person is being sexist. While I always use "folks" just to avoid the hassle, personally I wouldn't be too bothered if the people who take "Hey guys" as a sexist insult don't talk to me.
I guess it is some kind of "gotcha", intended to undermine "woke" people but it seems a bit self-defeating.
"White people are so racist they're even racist when they're trying to be non-racist" seems more woke than anti-woke to me, but that doesn't seem to be the intention.
Is there injustice in the world? Clearly. Are these people insufferable? Also very much yes.
In the tech context specifically, we are very international in a way that doesn't map to US culture wars, which makes the white woke people look even more out of touch with reality.
And since the negative discourse (e.g. saying "Women face so many issue in the workplace" as a man) is way more socially palatable than a positive one (saying "Women have it OK now in the workplace" as a man), people who try to be sensible about thing not directly concerning them tend to overdo it by amplifying the "everything is bad" angle.
Which is why at the height of the BLM movements, lots of well-meaning (but IMO severely misguided) people felt that 'master' or 'blacklist' were carriers of oppression, while not thinking twice about words such as 'white noise' or 'white-label' (Implying that a lack of creativity or panache is associated with whiteness, The horror!), The former was among white 'wokes' sensibility-by-proxy, while the same crowd had the experience and tool to know this argument is bonker, and that anyone having issue with the expression 'white noise' has mental issue.
I came to this conclusion after a gay/muslim friend of mine, who likes to do humoristic quizzes on Instagram did one for the Ramadan. He asked "Apart from Ramadan, what are the other 4 pillars of Islam", and accepted the Ru Paul reference "Creativity, Uniqueness, Nerves and Talent" as the answer. The only people taking issue with that were non-muslim white french dudes who felt it was islamophobic, which greatly annoyed my friend, who felt it feed into the stereotypes of "angry muslim".
I'm a native English speaker in the US, in my late 50s, and I was taught that "guys" used in that way was gender neutral in grade school.
It seems very reasonable that "guys" could function similarly in English. Moreover, I might not say "the guys I've dated" as a straight man, but if all the women I've ever dated were talking together in a room, I wouldn't bat an eye asking "what are you guys all doing?".
Similarly, I wouldn't say "all the folks I've dated", but I might say "good evening, folks" -- the word is a misfit solely because of the idioms and context, not because the word is inherently communicating something else.
Like in those earlier examples, the people are probably all within the same house/yard at the same time when they're called to dinner, or they're all using the same online discussion forum at about the same time.
When discussing multiple individuals with significant time and/or distance separating them (like the people somebody has dated over the span of years), a more specific term like "men", "women", "men and women", or "people" would likely be used instead.
In any case, I think your example works better with a bisexual speaker. A straight guy would probably use more specific gendered language rather than a neuter construction. A bisexual person using "guys" to refer to the men and women (s)he has dated would be an example of a third person neuter usage—which I also think would be quite rare.
I wish you guys could understand that
The rest of the comment is speculative: you don't know anything about their politics, or have any reason to believe they're being obtuse.
Even that's a weak rule though. For example if a girls soccer team performed really well you might hear someone say "those guys really gave it their all today" (though I'd say this usage is mostly dead, I don't think I've heard it this way in a long time), but never "THE guys really gave it their all today".
I'm sure some linguists have studied this and have a term for this kind of thing.
I absolutely would not say "hey ladies"
It would feel too formal to say "hey everyone"
"Hey people" would be awkward
"Hey you all" eh
It might be better to leave it at "hey"
It might be best to just say "bye"
The idea of a native (probably white) English speaker lecturing them on it being sexist or non-inclusive is repugnant to the extreme. At that point they've lost the argument, and can frankly get fucked.
It really is amazing how those people don't see it that way and instead think they are really helping anyone. English was forced on a lot of the world. Now it's sort of happening again, in a different way and with infinitely less violence, but the justification remains the same: to civilize the savages.
So it's definitely whiplash inducing for the same group of people preaching inclusion and tolerance, and how we need to accept regional and racial dialects in the workplace, to then turn around in implement slackbots that nag and shame me for my regional speech patterns.