The site is pretty clear: "Free and works in browser", "Processed locally", "Private". But apparently the site (sorry for the harsh word, but I can't interpret it any other way) lies.
"is incorrect" is slightly less harsh, but in this case, I'd call it a lie. It's a rather subtle but important implementation detail. I don't think the author (who is here in this thread) is necessarily malicious because of this, but, well, it's a lie.