The context here is with a locked vault so no data to auto-fill with. It's most likely purpose was to indicate "LP has the login info for this site but the vault is locked". An indicator like that can be coarse and simply use a root domain and ignore subdomains and paths, better to have some false positives than leak data in the clear.

[We might be wrong about the locked-vault but might have data scenario, but that kind of seems the only legit reason to store that stuff in the clear, so if that wasn't the reason, LP's negligence is even worse]