Or Apple set a star rating at the album level. I've never set a star rating for an album and yet, they're there in iTunes. Been driving me nuts and messing with my smart playlists for at least a year...
Same here, so I modified my "Recently Played" smart playlist in iTunes to put the Last Played and Album Rating columns all the way on the left. I then periodically scan my recent plays for solid (black) Album Rating and null them out by clicking just to the left of the 1st star of Album Rating. For me, what seems to be initiating the solid Album Rating is when I re-rate a song on my iPhone and then re-sync. The rating change sticks, but then applies a solid Album Rating to the album of the song. Irritating as hell, but at least I can now see and correct this.
Oddly enough, it doesn't happen to all songs that I re-rate on my iPhone, and there's no pattern between ripped albums vs. purchased albums. This all started when I dabbled with iCloud Music Library when it first came out. I quickly abandoned it when it duplicated all my playlists and wiped out all my song ratings (I recovered my .itl file from Time Machine). Since then this problem has plagued me, though I can't say that the specific steps I took are the cause. I do think it has something to do with Apple Music (I'm not a subscriber) and/or iCloud Music Library, like something Apple did on the backend that is affecting behavior in iTunes.