I looked at Catija's profile and noticed that she was a staff member. I also noticed that all of the communities she was part of (even the one's with just 101 default rep), she was marked as a moderator. This brought a question to my mind: Are staff members marked as moderators for every site they join? Or is it just specific staff members?
Community Managers get mod diamonds by default on every community. Not all employees get mod diamonds and not everywhere - they're given out as needed.. Community managers... well need them a lot of the time.
There's also an employee or two who're proper site mods on specific sites as well, from before they were employed.
The's a separate "employee" flag in the API that wasn't exposed on the website until recently, so at least in theory you can tell when someone is an employee, whether or not they have a diamond