You’re right.
https://github.com/hzrd149/nostrudel/blob/9756a2eb6eb90c42465079d0d38f3cd50c797b97/src/views/user/muted-by.tsx
It’s apparently querying pubkeys in the unencrypted sections of kinds 10000 and 30007 events. I just wrote a script to do something similar and found a single person publicly muting me 🫡🔇.  Somehow, I’m too dumb to find this page in Nostrudel's UI.
nostr:nprofile1qqsq6pjgpvxxuwlrexs6vht7d0pqjy3864dlf3m7adsr0wnhwmpspmqpzamhxue69uhhyetvv9ujumn0wd68ytnzv9hxgtcpzdmhxue69uhhwmm59e6hg7r09ehkuef0qyt8wumn8ghj7mn0wd68yetvd96x2uewdaexwtcvw5g7s, if you’re curious, my script found 53 people publicly blocking you (DM me if you want the pubkeys :).