I haven't read the novel, but going by the Wikipedia article you could argue that just because it features astronauts on the ISS doesn't yet make it science fiction - as long as nothing unusual happens to the astronauts, what goes on on the ISS is no more science fiction than what an airline pilot does in their day-to-day job.

Even the author seems to agree (also from Wikipedia): "In an interview, Harvey stated that her goal was to write the novel as a "space pastoral", focusing on realism and the beauty of space rather than the speculative nature of science fiction."

Yeah, the key distinguisher for "Science Fiction" is that it asks a "What if?" question. Some SF authors (e.g. Margaret Atwood) don't like that because they're writing novels with no robots or spaceships, but too bad, you don't get to choose how other people experience your work.