When it comes down to it, the very old man with enormous wings is an outsider, a foreigner, a stranger, and—we say this lovingly—a weirdo. He's not like anybody else. He talks funny, smells funny, acts funny, and did we mention the wings? The way he is treated has everything to do with his "otherness." No one knows how to treat him, or at least they act like they don't know how, because he's got wings. But what if he didn't? Do you think the community of "A Very Old Man with Enormous Wings" would treat a normal, wingless old guy who wandered into town the way they do the angel?
The townspeople's cruel treatment of the old man is a criticism of the way societies tend to treat outsiders.
The townspeople are driven by fear of the unknown to keep the strange old man caged up.