I didn't assert that assuming 'that it's real/true to them unless I have reason to think otherwise' requires a lack of critical thinking. You're critical thinking comes in when you see someone that you suspect is being dishonest. You're not just sitting there going "Lalala, everyone means exactly what they say all the time because thinking anything else would be judgemental."

And you are thinking in terms of someone claiming to be something verses someone experiencing themselves as being someting. When you think people are being dishonest, then you think they're claiming to be something they know they're not. Ordinarily, though you view people's statements as honest descriptions of their experiences whether those experiences are literally real or not. But that's starting to get into differences between when one person would think, "I don't believe you" and someone else wouldn't and I don't really want to go there because it only leads to drama.

It's not a matter of whether or not anyone thinks the person(s) should be told that you don't believe them or something should be done. That's an entirely different discussion that would also lead straight to drama.
I'm only interested in what people think when they do run into statements that, for whatever reason, they can't or don't believe. It's just interesting seeing people's different responses because we ourselves have different responses.