[CaliforniaKarl]

There is no "US capitol exclusion zone" as such. Instead, there are two things:

• A number of Prohibited Areas, of which P-56 is the one covering the capitol. That is the "prohibited airspace" that the plane avoided.

• The Flight-Restricted Zone that extends 15 miles around Washington National Airport (DCA).

If you go to http://vfrmap.com, search for "KDCA", and switch the drop-down menu to "Sectionals", you'll see where the stadium is relative to P-56. See also https://www.faa.gov/newsroom/restricted-airspace-0

Though in this case, I believe both DCA Tower and Approach were aware of this operation, and so the pilots are OK, just the Capitol Police didn't get the word. I'm certain they have radar (or at least a radar feed), and so would have been justifiably concerned.