I think the crux of this claim depends on the fact that most military jets have only a supersonic dash capability. Staying supersonic for more than a few minutes seriously depletes their fuel reserves which are not particularly generous in the first place.
Also there are few places for them to go and play at Mach 1 plus.
So the vast number of supersonic capable military jets spend little or no time in that part of their envelope. Whereas Concorde spends somewhere around 80% (at a guess) of its time supersonic, for hours at a time.
I would be prepared to believe that boast.