It seems like "Byzantine" is just an unfortunate label, which should be "church music", but if you expand it you will see that byzantine chant is present.
It's still too broad. Byzantine chant is an entire discipline in itself, and so are a bunch of other categories included in "Church Music". There's a category for Anglican choirs, so why not for Russian "Greek" chant or Kievan/Znamenny Polyphony? There's a lot of territory here.
The way this concept would really work, in practice, at a streaming service is as the basis for some kind of cluster analysis that could predict what you might want based on your listening behavior and that of others "like you".
Having people use words to precisely pin-down entire genre's is perhaps near the end of it's usefulness.