How can you say that apaticular religion is actually a religion?

Religion is a strong belief in a supernatural power or powers that control human destiny. For instance, Christianity is a religion because Christians believe and worship a supreme God that created everything. There is much more to Christianity than that, but that is the basic belief. There are several major religions around the world, including; Islam, Buddhism, Judaism, etc. But this is just an example.

Or you could look at it this way...

How can you say any particular dog is actually a dog? You just know it is a dog. That is how it's classified. It's obviously not a cat. Although some dogs seem pretty debatable. You can replace the italicized Words with any noun. It is just a way to help understand the original question.