This isn't just a Frendica thing; you can see this from Mastodon, mbin/kbin, etc. Many people seem to think upvotes and downvotes are private, but the reality is that they're publicly available information by default in ActivityPub. Lemmy just hides the information on the front-end for "normal" users; If you're a moderator you can clearly see everything.
If one wants truly pseudonymous voting, they're free to try out PieFed. See the announcement post for this feature for more details.