[Marsh.]

Originally Posted by Kazanne

https://www.urbandictionary.com/define.php?term=sure, jan

"Sure, Jan" is used when you can easily read a family or friend for the filthy liar they are. You say it when you obviously know they are lying but you don't want to ...

It's from the Brady Bunch.

It means you don't believe what's being said.

That's not accusing the person saying it of being a liar but they've been misinformed.

Since Chuff has never seen this cafe, she's been misinformed rather than lying.