We really need to know how you structure your custom fields in the release CPT. I simply assumed in the release CPT you have a custom field named album_artist which is a text field that holds the artist’s name. If so, then it was correct to match it with the title of the artist CPT which is also their name.
Release CPT
Post title: Death Magnetic
Album title (album_title, text field): Death Magnetic
Album artist (album_artist, text field): Metallica
Artist CPT
Post title (the_title()): Metallica
So, meta_key => album_artist = the_title().
Really, you just need to find what values you can match between your CPT and you’re all set.
