Is this site on a “managed” WordPress installation?
On that type of hosting plan, the host takes away certain admin capabilities, so they can run the updates without the admin interfering, so Wordfence sees that the user is not a full admin. If that is the case, we do have an open bug report to be fixed in a future version of Wordfence, to identify the admin by another method.
When it is fixed, you should still get the alert emails so that you would know if someone did find a way sign in as an admin, but the emails should identify you as an admin instead of a non-admin. (This alert is helpful if the site is ever compromised, but you can disable these login alerts under the Alerts heading on the Wordfence options page, if you do not want them.)
-Matt R