Mach 5 is closer to 4,000 mph... that's nothing to sneeze at given the forces acting on the surfaces and the friction on the skin. What's unique here is that they were testing a SCRAMjet which essentially uses the shockwave of the air for super compression and then ignite. It's a RAMjet on steroids. Theoretically, it could reach speeds up to Mach 25 with enough fuel.
By contrast, the SR-71's turbo-ramjets used the cone on the front of the engine to bifurcate the shockwave and prevent it from getting inside the engine where forces would have reeked havoc on the fan blades. At speeds above Mach 3, 58% of its thrust could be from the pressure of the shockwave in the nacelles. Most of the operation of the SR-71 engines happen at subsonic air speeds.
Recently read a book about the X and was shocked to read that they were doing SCRAM tests way back then with a test fixture mounted on the lower tail fin or whatever it is called and was jettisoned just before landing.