I don't think "please don't sneer" means "forego all metacommentary," and I didn't interpret this as particularly sneering or mean or rude. Cursory inspection of dang's citing this rule seems to be really broad, really rude snark, I don't think this comment fits the pattern I'm seeing there.

I'd propose our discourse would be hobbled if we couldn't make comments like, "many people in this discussion have misconception X". But perhaps "very wrong mental model" was too many superlatives and "misunderstanding" would've been sufficient.