No. NIP-51 clearly defined that private mute list (tags) should be encrypted in "content" event field
https://github.com/nostr-protocol/nips/blob/master/51.md#encryption-process-pseudocode
Amethyst for example has done that properly by encrypting the tags in content field
AFAIK, Snort support both public and private list. Block button for private list and mute button for public list.