Interesting move. Warner Music Group comment on the sale:

This sale has nothing to do with our view of Spotify’s future. We’re hugely optimistic about the growth of subscription streaming, we know it has only just begun to fulfill its potential for global scale. We fully expect Spotify to continue to play a major role in that growth.

Odd to get out if their confidence is so high. I found the logic confusing. You can read more about the WMG earnings call here.