As far as I can tell all Spotify's playlists (in all forms, e.g. including "random" and "track radio") use weighted algorithms based on several factors like user's play history, Spotify's recommendations (probably includes paid promotions), general artist's popularity, etc.

When I still used Spotify, I would get a dozen of my favorite artists mixed into basically any "playlist" I pick. Was one of the reasons I quit Spotify - they are too opinionated on what I should listen to.