I don’t think that Joe is doing any noseguarding. Given that he is an Orthodox Jew, he is probably following the law regarding gossiping speech. Gossip is not inherently a sin according to Jewish teachings, but lashon hara, malicious gossip is a sin. Lashon hara would be gossip, whether true or not, that negatively harms someone in a physical, financial, or mental sense. It is considered a very grave sin.
The revelation that Mandy catfished Rekieta undoubtedly caused harmed to Rekieta. Whether or not he will learn from this error is to be seen. Joe probably feels some sort of guilt in accidentally showing Mandy’s phone number, contributing to this drama, and potentially aiding in what could be considered lashon hara.