I don't think the course itself breaks any criteria. It was just a big loop, so any slopes or tailwind would not help the runner. "Each lap of the course featured two 4.3-kilometre (2.7-mile) out-and-back stretches... There is only 2.4 metres (7.9 feet) of incline over the entire route."

https://en.wikipedia.org/wiki/INEOS_1%3A59_Challenge