Except the moths don’t usually land on tree trunks in nature. So yeh, the entire experiment is flawed. Its still makes the cut for being some of the best evidence for decent from a common ancestor despite being meaningless.
You don't suppose the rest of the trees were affected by the soot of the coal age do you? And yes, birds for which the camo would matter, are not the only predator that east moths, but they do eat them.