I have heard a number of people dispute/ridicule any thing above mach 3 for the SR-71 no matter what some article claims. 5760 mph (1.6sec/mile X 60seconds X 60minutes) is something like mach 7.5, which would have made the plane hypersonic.
7.5 is not simply above the 3.2 limit, but astronomically above it.
Maybe that pilot who wrote the article may have made up the number or accidentally revealed the real number.