Still that does not provide proof. If anything it goes in the opposite direction. In the run up to dropping the bomb, the 509th had had to deal with leaks, security risks, and curious snoops. They developed both security measures and disinformation techniques. They would never have simply released details about a flying saucer. The level of classification would have been extraordinary. But they may have created a disinformation to cover something else, like the high altitude baloons being deployed to observe Soviet atomic tests.
I think your assumptions are far from . . . fool proof.