I think it plays on the fear society has of big people: Fear of being seen with one, fear of becoming one.
The fact that there is a sign warning people is what did it for me. The notion that 'fatties' are this dangerous thing that could fall from the sky and destroy civilization mark this as absurdist parody for me. Kind of 'Chicken Little', in its way.
Not absurdist parody at its best, but pretty clever.
The unattractiveness of the falling fatties, as well as the stereotypes attributed to them (the bikini-clad woman with the ice cream and fries, the guy with the sleeveless tee drinking a beer, the bad skin on the kid with the KISS hat) appear to have been included to mock the views of those (like the book-reading character in the comic) who view fat people as a threat.
Think of this situation in real life: A place where fat people are known to be has a warning posted, to protect folks from coming into contact with them. That's not too far removed from reality. Then, because it's a comic, crank up the preposterousness of the idea to show what a ludicrous concept it is in the first place.
One of the things I do like about it is that the falling fatties seem to come from all walks of life (along with the poorly-dressed are at least one man in a suit and another with shirt and tie).
Also, the fact that this walking guy was blissfully in his own little world before encountering this situation, and is so stressed once it starts happening, speaks volumes.
The little guy, to me, represents mainstream media: All wrapped up in himself, unaware of anything that exists outside of his cocoon. Suddenly, fat people become his biggest problem.
Fat people. Not war, the economy, world hunger, poverty, disease, or environmental concerns.
Isn't that what we've seen on the covers of tabloid magazines for decades now?
So, yeah. I think it's parody, mocking the small-mindedness of those whose biggest fear is fat people.