Why was this commercial jet accompanied by small plane near Seattle? From the South Beach Campground on the western shore of the Olympic Peninsula in Washington State we observed this unusual formation:



I only had a Sony RX100 at hand but perhaps the image quality is sufficient to recognize the airplanes.

The picture was taken on July 23rd, at 20.20h PDT (the image timestamp is 6 minutes off), looking roughly NNW. I don't dare guess the altitude, but to the bare eye the small airplane was a mere dot. The two planes flew in formation in a circular counter-clockwise pattern around the north-eastern part of the Olympic Peninsula. They re-appeared two or three (I think three) times. They appeared to fly at low speed. 

We realized that we were only approximately 150 km west of Seattle, the Boeing headquarters. Was this a test flight? Which planes are involved? What is the function of the small accompanying jet?
It's a Fedex 777F N894FD in (probably) pre-delivery aerial photography/test flight accompanied by one of Boeing's chase aircraft.

After some maneuvers (shown below), the plane headed to MEM, Fedex's "SuperHub".


(Source)

The flight on flightradar24: https://www.flightradar24.com/2019-07-24/03:16/12x/FDX9032/2168b4b1 and flightaware: https://flightaware.com/live/flight/FDX9032/history/20190724/0215Z/KPAE/KMEM