More specifically, is there anything about texture atlases specific to textures? From what I've read of them, they might just as well be called image atlases. Images are not the same as textures, but textures can be created out of images.
Because whoever coined the term in the first place was using the technique in a way related textures, in all likelihood. The term is quite old and well established that it isn't even cited in research papers any longer, and hasn't been going back some years.
There's nothing specific about the technique that really applies to textures. You could just as easily use it for image data that isn't going to be used as a texture in 3D graphics. In fact, taken to logical extremes, the basis of the idea is to pack smaller instances of a thing into larger instances of a thing to optimize for some constraint. We do this often in other areas of software engineering. For example it's the basic technique behind creating "pack file" archives of all a game's resources.