I have my own playlist containing over 7K tracks.
Sometimes I only want to listen to tracks from one artist, back to back within this playlist.
I go into my playlist and search for the artist. Up comes the results, only displaying tracks featuring the artist I have searched for. So far, so good.
I tap on one of the songs and listen until its completion. Spotify then plays another song that doesn't contain the artist I have searched for (i.e. one not listed in my filtered results).