Sounds like you were in the "zone". It's that feeling you get when everything is right. It's an amazing feeling.
I had a similar experience walking through Kamakura listening to Shapeshifter NZ's "Drive" this summer. I was enamored in the moment and there are few things quite like it.
I honestly think it could be tied in with superstring theory, that everything is connected. Sometimes we tap into that connectivity and experience that euphoric feeling. Or, maybe it's just a serotonin dump...
Haven't heard Belle & Sebastian since the late 90's! Nice choice.
I wasn't quite in the zone, but I've been there before. It is a great feeling. Something about that song just does it for me, and the weather corresponded.
I don't know much about string theory. It seems like an interesting correlation. A friend recently posted an article about how most people don't get goosebumps from listening to music, about how that is a rare phenomenon. That really surprises me. For me, walking around or riding with headphones on is transformational. Maybe that has to do with experimenting with things in my youth, though;)