Do you have a ‘Smart TV’?
Does your TV have connection to the Internet via WiFi or phone line?
Does it have BlueTooth?
You could be getting text messages sent out that are not intended for you.
Since it was not on the screen when you rewound the TVR, it was probably sent thru the landline or WiFi connection..............
No WIFI, that's not enabled, but it is connected via Ethernet. No BlueTooth or phone line either. It's possible it's coming through the Internet though. . . or riding on top of the Video signal from Comcast. It is a "Smart TV. . , and a 3D TV. So it could have come through on the left or right eye channel.