Many don't come back because they aren't here to join, they're running a phishing scam. In this case, they wanted you to private message them and then they could take it off Tnet and begin the QR code scam. ( i posted a link about QR scams previously),
Basically, the scam works like this:
"You message him and then the scammers can send an email, text, share a flyer or send a piece of mail that includes a QR code. The victim scans the code with their phone’s camera and opens the link.
In some scams, the QR code takes the victim to a phishing website where the victim is encouraged to input personal information or login credentials for scammers to steal. In other scams, the QR code makes the phone automatically launch a payment app or follow a malicious social media account.: