Aren't there restrictions on how close to a Royal Flight another aircraft can get? Guess not looking at the picture but it seems a bit strange.
Such rules are for potentially "bad guys". It's a common procedure that heads of state on official visits are escorted by fast jets of the host government in their airspace. They make the rules there. And the dedicated professionals who fly those jets in formation have been trained and screened and checked over and over again to the highest standards...they're not the potentially bad guys you need to keep away...