I think everyone knows what is meant by an unemployment rate for a particular class of workers.
No different than rates for service workers, manufacturing workers, and other categories.
Be careful with your own statistics. "Government employment" is down only if you include state workers.
The big spike is census workers. You get a spike like that every ten years.
(Edit: replaced graph with a locally-loaded one. Don't trust FRED link to last. Also stretched out the bottom scale.)