To read their comment generously as I did initially, calling it a "quote of hearsay" is calling the validity of the citation so far removed from being trustworthy it doesn't deserve the word. Granted, it would be doing this without explicitly stating so or supporting it with any evidence or arguments.
To be honest, I'm not convinced by this source. We don't know who made the claim, we know a guy that wrote a DnD book a year and a half ago told a youtuber they exist and said it. That's a step or two removed from where I would trust it.