“suppose you could also say it is “fat shaming”-- because aren’t they implying that fat people are not attractive to sexual predators?”
No, they’re implying that fat people would be harder to overpower / drag into a car.
They AREN’T fat shaming because they WANT people to be comfortable with having a few extra pounds (from eating their delicious pastry). Fat shaming would be making fun of people who indulged too much. They are doing precisely the opposite.