TV turns off with XBox even though they are not connected

A little disclaimer first, I haven’t actually seen this but my son is telling me all about it. He has his XBox hooked up to his TV and it used to be hooked up to his mother’s. When he shuts his Xbox off it shuts off her TV also. It doesn’t matter if he shuts it off by the controller or power button. I thought you could only control the TV through the HDMI, can it do it over wifi?