Nevermind the ATSC 3.0 theory unless you are looking at the Fox or MyNet signals from Buffalo. rabbitears.info shows all the Toronto stations are all 1080i with one 720p. Don't know ...

Or possibly watching an ATSC 3.0 channel (channel number greater than 100) and recording its ATSC 1.0 simulcast channel. Could be watching an HDR enhanced 3.0 sports program, for example.

Maybe watch/record and compare a channel you know to be SD 480i and without an ATSC 3.0 option - a brightly ...