I seriously doubt the post office had much to do with tracking him down. My repeated experience with the USPS is that they pay absolutely no attention to mail forwarding requests, ever. It's far more likely that someone at the matching network did some googling.
And I don't need a new phone number, that's kind of the point. I can switch providers and still keep my number. I can move to the other side of the country and keep my number. That's what I want out of the post office.
I've wanted that for years from the post office: one address, your stuff follows you wherever, you never change your "address" you just update your location with the post office. I explained the idea to my first wife in the late seventies, and she thought I was solving a non-problem.
Some mailbox companies do that for you. People (esp old folks) living in RV traveling don't have physical address, so they set up one permanent address with a mailbox company to receive all incoming mails. The mailbox company would forward them to their current location. Whenever they stop at one place extensively, they contact the mailbox company to update the mail forward to the new location.
And I don't need a new phone number, that's kind of the point. I can switch providers and still keep my number. I can move to the other side of the country and keep my number. That's what I want out of the post office.