Yeah, it sends a message to that number so they can call you back and connect your call, presumably.

I think that it said that a message was sent FROM his phone. You can view all messages (to and from) through voice.google.com.

"from my phone to a VoIP number 760-537-0537"

Sent from his phone to a Google phone number. Presumably he noticed it in his SMS app after it was sent. Or maybe noticed it on his phone bill.