Not just being flippant; I’ve seen over the years TV linked to just about everything.
It makes sense a family that lets their family watch TV would have a more sedentary lifestyle. But the study isn’t advising a particular amount of exercise or whatnot, it’s just advising limiting the amount of TV.
Then there’s the socioeconomic class issue which has enormous effect on junk food/academics/etc. (and families which can’t afford to do much watch TV more), which I’m hoping they accounted for, but given my experience with these studies I doubt they did.