There is application of science (or technology) in collecting and calibrating the data. Presentation of the data is art.
Here is my rationale for categorizing it this way. When we capture the data, there is more or less a "right" answer. Stars should be round, with a proper brightness profile, and they should look the same everywhere in the field. We talk about sources of noise, how to make some of them, such a read noise, irrelevant. We quantify things like seeing and star elongation. When we calibrate images, it is with the goal of removing artifacts introduced by the equipment. At least for me, there is a "right" result for the master frame for each channel. In my work, I can typically get to channel masters that look great. And then it all goes off the rails...
Once the channel masters have been created, it ceases to be science and becomes art. The astrophographer as an idea in mind as to how the background should look, what parts of the subject should be enhanced, and what parts should be de-emphasized. Color tones and saturation are generally processed to bring them closer to the astrophotographer's idea of what it should look like or what they want to show.
I'm a huge fan of Adam Block's tutorials. One of the things that he talks about on his image processing walk through videos is the story that he wants to tell with the image. For example, he has a tutorial walk through of the Crescent Nebula. He talks about wanting to show a "Jellyfish in a Cosmic Sea". As he makes decisions in processing, he'll refer back to the story and how it affects his choices. I've also seen where he'll notice some small detail in the data that most of us would just skip over. He'll sometimes process the image to enhance that aspect, which makes his work unique as compared to countless other images of the same object.
I mainly call this out because it's something that I would have never considered, had I not used his tutorial materials. Even though I am aware of how he's doing this, it's completely unintuitive to me, and I don't feel like I've ever successfully applied it.
And while I'm at it, I'll give one more example that involves portrait photography. My wife has a friend who had an interest in doing portraits. When she was getting started, she frequently had me help here with the technical aspects of how the camera works. With a little bit of technical knowledge, she started making photos that were simply stunning. She looks at subject matter, framing and lighting completely differently than I do.
I suppose that since my artistic talent is minuscule, compared to some of these other people, I recognize the art in the end result that typically escapes my attempts.