You do know that being on TV adds 5 pounds to the subject and HDTV adds even more? That is probably what you are seeing!😄
The average size of fox and grey squirrels may be a little larger than states further south but I think the larger appearance may be due to more adult squirrels available than other places as squirrel hunting is not nearly as popular up here as it was when I was a kid 40 years ago. And it wasn't as popular as a couple decades before that. Our season also begins in mid-September which gives the young a bit more time to grow compared to some other states where the season opens earlier. We tend to have a max of 2 litters a year rather than 3 which, coupled with a later season, adds up to larger squirrels over all.
Depending on where they are hunting, squirrels might be bigger too. Get in the agricultural zone where corn is king and squirrels look to be heavier than in more wooded areas where squirrels depend mostly on mast for food. All those carbs add fat, just like with people.
A little heavier coat might make squirrels look larger but I can't say I have really noticed this. It makes sense but when one sees them every day, this type of change is pretty subtle so isn't noticed easily. It is very likely positioning for the camera is also possible though that seems pretty obvious when seen.
I don't think squirrels up here are genetically bigger than those in other places but there may be some other reasons that allow more squirrels to reach their full adult size. Plus, some positioning for the camera is probably done.