This type of ic story is frowned upon. However, as Wichita has said, other characters are most likely to think of them as insane, or ignore them completely. (Okay, so some might actually believe the story, but that's their perogative

This belief should be kept as private as possible, imo.)
From a PD perspective, it's a fine line, as Julie2 has indicated. Spaceships and aliens should not be used, as these concepts are beyond the comprehension of Cantrians.
Being brought forth into the world from a uterus is just plain ludicrous (from a Cantrians perspective), though as other body parts are assumed to exist, I don't see why not a uterus. Cantrians just wouldn't know it's purpose, as they are all spawned, not born.
That someone claims to be descended from anything is also ludicrous, and a concept unknown to Cantrians. Yes, the fellow is clearly insane. A CR breach? Borderline, but not serious. The biggest being the mention of "planets", which is not something that is normally assumed to exist beyond the Cantr realm.