Ask HN: How random you think Spotify(or companies with user data) is?

Hi HN, I have a question! As you know you can listen Spotify playlists in a "random" order. I've been wondering about this lately and I don't think there's any chance that these randomizers are implemented using regular rand() functions. Do you have any experience/idea on how these random functions are implemented in companies that have massive user data? What factors they take into account?