I'd be of the opinion that a persons interpretation of the sound is
what makes it music, to them.
Yes, but you're doing something to the sound in your head. You are
making it into music by attaching a "story" to it, or a "meaning", or [I
don't really have the words]. In a way, when you're sitting on a train
and it's making funky rhythms, and you're hearing it as music, really
you're being more of a musician than a listener, because you're making
it into music in your head. I think part of this is seeing potential
for a "story" in the sounds you're hearing. So, in short, what you
heard was not music till you processed it so you hear it as in a way,
sounds made intentionally, as if there was a purpose to them or a
message in them.
(Btw, I hate trying to put this stuff in words because it's guaranteed
that I'll use the wrong ones just because I can't think of decent ones,
and 99% of the time my meaning gets lost. Some people are good at
talking about music though.)
Jamil