I didn't hear it anywhere, its personal experience. Spotify straight up isn't shuffling any of my older liked music. Everytime I hit shuffle it always ends up localized around recently saved music and it never changes. Moreover, that's a blogpost from a decade ago. Spotify changes stuff constantly. I seriously doubt that is the same algorithm they're using now. ESPECIALLY considering they've introduced 'Smart Shuffle' which doesn't only shuffle music you have saved but adds completely new music into the mix as well. That and Spotifys overall quality control has dropped drastically in the past decade.