I'm not sure it's that puzzling - they wanted liquidity, but don't need any more cash so don't want to dilute the existing equity.

Also worth noting a stat lower down the article that's a different point of view to the "down 10%" of the headline:

'$132 was used as a “reference point,” valuing the company at $23.5 billion. Since there was no IPO price, that demarcation is being used to say that Spotify traded up about 13% on its first day.'

Credit to them for doing something non-typical that fits what they needed. It seems like it's gone according to plan so far.