It was the scientist who proved he could fly. The religious person made the same claim but didn’t even try to prove it.
But the scientist and the religious person are shown to be identical, and the first row showed that he could fly. I.e., the claim that he refused to prove was implied to be true, regardless of his refusal to prove it.
You’re interpreting the artwork too literally. I think the creator was just trying to save themselves a bit of drawing time.