I've created 4 free accounts over the years but haven't spent a minute listening. I'm sure it's like facebook, once an account is created it's counted as a unique user forever.
That’s ok, but they confirmed they have around 250mil paid subscribers. I can easily imagine 350-400mil free ones on top of that, especially since they explicitly say they only count active users, not just the number of user accounts.
Well, they'd need to cite something that shows that every Spotify member shares their membership with 1.6 other people. I'm skeptical of that. It's bad enough with Netflix recommendations and profiles - Spotify doesn't support profiles, so you're sharing your music choices with those people? Spotify is also pretty aggressive with account sharing.
More likely free users with their own accounts. Subscribed users are a subset of all users and I wouldn’t be surprised if unsubscribed users were the larger group.
[1] https://newsroom.spotify.com/company-info/