The comment it's replying to stated that 1937 quote as if they had checked it. That deception seems ruder to me the language in the comment you're talking about. But I do agree the last sentence could've been omitted while getting the core point across (but we're all only human).

Not rude, just direct.

Agree that the post comes across as rude in tone, but it’s never explicitly disparaging. Might just be an overly direct tone (non-native English speaker, or maybe on the spectrum?)