Hes not even a Diplomat... ??
Diplomatic status, having a Diplomatic Passport and accompanying Pakistani Visa with a future expiration date are what any and all Amricans, career employees or contract employees, have in the service of the US Department of State.
There are two main career tracks in the US State Dept. one of which is now done sometimes, in part, based on overseas locations, by contract instead of career service employees.
1. So called "Diplomats" are in the US Foreign Service and are Foreign Service Officers, which includes the most senior rank of being a US Ambassador.
2. Diplomatic Service includes US Department of State Consular Services employees and contract hired related personnel as in this case Security Consultant or Service Performance Personnel.
Both these two categories have DIPLOMATIC PASSPORTS...don't confused the term Diplomat with the broader term Diplomatic...both categories have diplomatic immunity.
3. A third category, which I was at the old Karachi US Embassy, are US military personnel who have Official US Military Passports. These folks, also, as I used to be one, ALSO have Diplomatic Immunity although we were not "diplomats" per se.
All three categories have "Diplomatic Immunity."
For other nations where the US has military bases run and operated by US Armed Forces you have In Country Status of Forces Agreements which lay out the legalisms and terms and conditions, and protections, for US military personnel serving in a particular, uniquely so, foreign nation with one or more US military bases.