All christian people, I have a question. Please help?

Idk if any of you guys have ever done or heard of this but im hoping from some answers. I have some christian friends and when It comes to the point of music they always say my music is christian music and how it uplifts the name of God so much. They sterotype EVERYTHING as Godly. I was listening to Lithium by Nirvana and they tried to tell me Nirvana was a christian band. They tried to convince me that mainstream rock is christian music since most of it does not conatin any suggestive language or lyrics. Why are they so blind to see that everything is not some type of christian thing.