Seriously, please don't go tell random people you don't know "pretty sure you've never X", especially if X is related to experiencing distress and/or a traumatic experience.

You have no idea whether they have. At best it doesn't add to the conversation, and at worse you're wrong and making everyone feel awful, yourself included.

The first comment about the bar being too low for PTSD did this too. Neither is helpful.

That's not a safe assumption to make.

What that would prove, even if it was true? It's like saying to someone who is arguing against the death penalty "you didn't have your family killed by a robber".

Even if that's true, that might make them more impartial and clear-headed on the issue, rather than less. The same reason that defense lawyers usually reject jurors that had personal experiences about the offence on trial.