It's the autoplay option.
"Autoplay takes the work out of choosing what to play next. Just play a song, then Autoplay finds similar songs and plays them afterward."
Play a song, then have similar songs autoplay. Or queue up music that you want to play next. Share control of your queue. And transfer your queue between your iPhone and HomePod so you can keep listening without missing a beat — all with Apple Music.
support.apple.com