It's called cognitive dissonance. None of these threads are legitimate.
If they make up bullshit about being 195 cm, or having extremely high IQ, and someone validates them, their brain will give them a dopamine rush even if it's all completely fabricated. The issue with these threads is that there is always an underlying ''concern''.
''Am I too short at 190 cm''?
I'm 190 cm, extremely rarely do I see anyone taller than I am. Apparently they live in a world where everyone are giants... if everyone are giants in our world, then that must mean they're pretty short, or at least very inconfident about their height