If you look at the formula speeds on speedsurfing.com, you should be skeptical of the claimed 35.5 knots. No one has come very close to that that speed on a formula board in flat water.
I have watched many formula sailors sailing in the 25+ knot speed range in very rough water, plus I have seen slalom boards in plenty of video and first hand in choppy water traveling in the 30 knot plus range. The video of the GO board looks nothing like 35 knots regardless of camera angle or telephoto.
He clearly got a spike or incorrect speed on his GPS.