From what you described, to an observer it would have sounded like you were arguing with them against the whole concept of protected classes, rather than pointing out that they should add ageism (etc.) to the list of things to be wary of.
Usually when people point out hypocrisy, people assume that they're making an indirect argument against the thing they're being accused of being hypocrites about. If you say something like "you seem to really worry about discrimination based on gender, but are ignoring ageism", that doesn't sound like you're trying to enlighten them about ageism. Rather, that sounds like you're trying to illustrate that the whole concept of protected classes is BS.
Accusations of hypocrisy are easily misinterpreted because so many people use them as a terrible form of argumentation. For example, consider all the people who get mad about other people complaining about intolerance, and the best they can come up with is "but you're just intolerant against intolerance!". As if pointing out hypocrisy invalidates whatever else someone is saying. It's the dumbest possible approach to debating an issue, but 99.9% of the time when I hear someone accuse someone else of hypocrisy, that's what they're doing. That may not have been what you were doing in that situation, but I could totally see how everyone might have misinterpreted you.