It's right up there with 'I've been clinically diagnosed with ADHD by a qualified psychiatrist and this medication has improved my life tremendously' -- 'There's no such thing, the medication doesn't do anything and you just need to mediate more, have you tried mindfulness?'

There were three people involved in that exchange, not two, assuming nobody's using multiple aliases...

crdrost described their vision problems, jbluepolarbear said "you have astigmatism", techrat popped in and said "[I have] no astigmatism" and jbluepolarbear made a more general statement that most people do.

I'd assume techrat doesn't know anything about crdrost's vision either.

Because nearly every person has some amount of astigmatism.