It's a centralized service, they just configure you account to be invisible in the search results of others.
And they don't check whether the file is really reachable. I've 'chmod 000' copyrighted files so they could not be downloaded (but still could be found in search), and Soulseek administrators were not happy with that ether.
I've been shadowbanned 4 times or so. They never unban, need new account.