Tracks and All Tracks are two table occurrences of the same data source table.
All tracks uses the X operator so that any record in the Music Library table matches to all the tracks records in the tracks table. Tracks matches track records by their record ID. Thus, when using the tracks relationship, the database only refers to the tracks that belong to that one record.
I suggest learing a bit about the difference between a table occurrence and a data source table may help you get started here: