Each song gets analysed and assigned ~10 audio parametres. If you tend to like tracks with, say, high danceability in the past X days, you're gonna get recommended more tracks with high danceability.

If you listen to a specific genre, it's gonna work great. If you tend to listen to unrelated tracks, your recommendations are gonna be shit. If you listen to a couple of albums that are really not what you listen to usually, it's gonna take you a while to get rid of similar tracks from your recommendations.

So to answer your question, it's more of a snapshot of the mood of the tracks you've interacted with recently, not your mood specifically.