I hadn't included "spotify" in my search, but I now see what you mean. I then searched for some tracks by my own band, and these too we "song and lyrics by" even though they were instrumentals - not songs - and had no lyrics.

It is obviously a label which Spotify seem to have applied when they really mean "recorded by". This is potentially misleading. I suspect most people will be searching for the artist rather than the songwriter, so it would make more sense and be more helpful if they said this.

Have you offered any feedback to Spotify?