Music Vibes & Free Writing

I was astonished today by how music choice may affect rhythm of writing. During first free-writing session I put classic "piano" instrumental, whereas the second session was accompanied by bossa nova beats. How so is music reflecting flow of writing? I sense that when I am writing with lounge music in any coffee shop feels drastically different from the same music, when writing in class. I sensed that my thinking process worked much better with piano sounds.