The little boxes in the corners with people's reactions is a very common theme on Japanese variety programming. People there like to see how minor celebrities react to what's being explained in the episodes. It's weird to us, but it's less obnoxious than our 90's sitcom laugh tracks were.
The translation was mostly to be expected. Nothing really derogative said. But it's pretty clear why they chose this person: they wanted the shock factor with the combination of ageplay and morbid obesity. Not blaming the OP for his weight, but the producers of this show for picking him.
Yes, Japanese people will act relatively reserved, but Elfking is correct. Japan is a very conformative, herd-mentality society and very few would be at all accepting of this, even with the excuse of hospital treatment for the bomb joke, or divorced parents, or an alcoholic, abusive father. There are pockets of exceptions in places like Tokyo, but that's no different than some place like San Francisco in the US.
As always, these shows continue to do us no favors. We're put on spectacle like zoo animals for people to gawk at. Heaven forbid they do a show about someone without a room full of adult-sized baby furniture, for-hire sitters, and BMI below 30.
Nothing at all wrong with the OP, his life, or what he's doing; but it's not at all representative of 90% of our community. It's very similar to how gays were always portrayed as flamboyant sex addicts in the 80's and 90's on TV in the US.
In the age of the internet, let's all just pray his classmates don't find this video online. It'll destroy his life.