SR-72 --- is the speed reported in this story wrong?
is the speed reported in this story wrong?

No
No it is not a misprint that the SR-72 is intended to be capable of Mach 6
From the horses' mouth:

Envisioned as an unmanned aircraft, the SR-72 would fly at speeds up to Mach 6, or six times the speed of sound. At this speed, the aircraft would be so fast, an adversary would have no time to react or hide.
The SR-72’s design incorporates lessons learned from the HTV-2, which flew to a top speed of Mach 20, or 13,000 mph, with a surface temperature of 3500°F.


Yes
Yes it is not true that Mach 6 is necessarily 4567.2423 MPH
From elsewhere:

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