Deleted on the server, not necessarily deleted in Sync. If you’d clear the data in the app and log in again, the comment would just be a normal deleted comment (“deleted by moderator” or whatever).

Before Sync came to Lemmy, it typically stood out because it would download a full browsable local copy of your timeline, and comments being visible that were deleted online were a common side effect of that. I guess these deleted comments still showing is just the classic Sync mechanism doing what it’s best at.