Compare this user's associated accounts with this user's associated accounts. The former includes a "No accounts matching this OpenID" message similar to what an individual user might find on their own account. The latter shows no such messages for the other sites.
The inconsistency of the message implies that in at least one of those cases, there is an account matching that OpenID that isn't associated. But if the user didn't want to associate accounts (and we are in fact allowed to manually do so), then why should Stack Overflow hint at the existence of sister accounts? I've spotted both kinds of display more than once, so neither version is limited to a single user.
Showing no message probably looks nicer.