Typically I agree with all the responses regarding "approach matters." If someone is also specifically asking for feedback about their type, also, then go to town in a helpful way in explaining your perceptions of the person's type. But otherwise, it can be a pretty ambiguous area.
It's like if you were walking around at a gathering and someone walks up and starts commenting on your clothing. "You can't really carry that off, you'd look a lot better in <this style> clothing unsolicited." or your hair style. Or your vocabulary. or your intelligence level. or some other random piece of data about you that you might not have been considering at the time and maybe weren't really expecting to be debating. It can even scan as, "Well, you say you're a Christian, or a libertarian, or [some other group], but I think you're really an [x]."
You guys know this meme? Depending on what you're currently doing, that kind of opening comment can be way off-topic. And depending on how it's delivered, it can also scan as invasive and judgmental and opinionated... and demanding.
Yes, it's a typology site, but not everything here and not every conversation is about typology. Also, not everything has to be public -- some interactions can be one-on-one.
If you're really curious about someone's type, maybe you could just say, "Hey, I see you are labeled as [type], what's up with that and/or how do you identify as that type?" IOW, ask the person questions to find out more why they think that.
And if you are really bothered (if for example you think someone is misrepresenting a type -- some folks do this regularly, saying, "As an [type], we always do this and this," which can be annoying if they do it a lot and you don't even think their type ID makes sense), you can also query them personally rather than making a public assault out of it. if they seem open to discussing it, then great.
People also are not obligated to engage someone who disagrees with them. Sometimes they have bad reasons for not engaging, sometimes they have great reasons. But again, this is why questions rather than confrontations are better. And like others have said, type questioning can also be weaponized, which isn't cool.
Just think a little bit about how you come off when you're engaging something that they might identify with or have possibly thought long and hard about already, esp if it's someone you barely know. Also, discussing something like this is more about making each other's lives better, not protecting turf.