What would make sense is to have a blacklist of usernames (like "admin" or "moderator"), then use the confusables map to see if a username or slug is visually confusable with a name from that blacklist.

I initially thought that must surely be what they are doing and they just worded it very, very poorly. But then of the 31 "disagreements" only one matters, the long s that's either f or s. All other disagreements map to visually similar symbols, like O and 0, which you should already treat as the same for this check

Not to mention that this is mostly an issue for URL slugs, so after NFKC normalization. In HTML this is more robustly solved by styling conventions. Even old bb-style forums will display admin and moderator user names in a different color or in bold to show their status. The modern flourish is to put a little icon next to these kinds of names, which also scales well to other identifiers.