On Disqus, the Username and Display name are separate, and serve distinct purposes for a user's account. The Display Name is what shows up next to a user’s comments, and does not need to be unique. The Username is a separate account identifier, and indicates the direct URL which can be used to visit a user’s profile.
What are each of the names used for?
Simple handle to easily identify the user in thread conversations
Does not need to be unique, so allows the user to be known by whatever name they prefer
Can be edited in the "Name” field in the Profile tab in Profile Settings
Identifies the unique URL at which a particular account can be viewed (for this reason, usernames must be unique)
Can be used in place of the account’s email address to log into an account
Can be edited in the "Username” field in the Account tab in Profile Settings
As Display names are not required to be unique, having the same Display name as another user is not in violation of Disqus’ terms of service. This alone is not sufficient evidence to support a case of Impersonation. If a user has the same Display name as another user, a duplicated avatar or corresponding post history that clearly demonstrates an intent to impersonate must also be present for action to be taken.