unfortunately there is no way to disable the matching
plex will forever try to match unmatched content
any random internet downloads, or bootlegs, or just a folder with your favorite files in it, that will never be a musicbrainz release, plex will always try to keep matching.
there is no way to turn off the matching, other than to switch off the new ‘plex music’ scanner/agent.
for example see @ Imported music tagged as Various artists
