While a reasonable principle I don't think it applies in context. People aren't expected to exhaustively source comments on HN. There's subjective etiquette to it.

In this case it would be reasonable to inquire about the basis of the original remark, or to reject based on personal knowledge, or to reject based on a concrete citation. But an arbitrary non-technical vibes based rejection doesn't fit with how things generally work here.

True but you can provide evidence to increase the quality of your claim.