My wife is bigtime into music. She advocates for music in the schools. Raises money for that purpose. Lobbies our state legislators to support music in the school system. Provides music lessons to kids. Organizes concerts for children and adults to perform in.
I do the same for mathematics and science education.
So yes, we *believe* music is important, and math and science.
But it's not a religion. While it's a "belief system", it's clearly different than a religious belief system. (Well, maybe not in the case of my wife and her peculiar devotion to certain flute pieces...).
"Belief" has several different definitions, and collapsing them to a single concept, while handy in the case of arguing religion vs. atheism, or faith vs. science, is a mistake, or a clever sophistry:
Belief:
1: a state or habit of mind in which trust or confidence is placed in some person or thing
2: something believed; especially : a tenet or body of tenets held by a group
3: conviction of the truth of some statement or the reality of some being or phenomenon especially when based on examination of evidence