To calculate true speed, turn radius or acceleration from an imaging sensor, an analyst needs geometry: range to target, line-of-sight rate, platform motion, sensor pointing, altitude/depth and timing data. Much of that information is redacted or absent from the public release.
The report’s 80 mph figure is explicitly estimated. Likewise, “just above the surface” is a crew description rather than a public instrumented altitude solution.
That means the 90-degree turns are meaningful as what the military operator perceived/reported, but the public video alone does not let an outside analyst prove an impossible or exotic maneuver.