It’s recordings of a composition. The left one with the disc is the number of recordings that exist overall, the one with the library icon is the number that’s in your library. Click on them and it will show you the composition with the list of recordings.
Sometimes they don’t show. There seem to be unknown requirements that make a track a recording of a composition, and the numbers only show if it is. Sometimes you can force it, but sometimes nothing seems to help. See here and the many other threads that are linked from there: