It’s a skill—I was browsing through some of the Strava activity of one of the top finishers who mentioned he had lapped a few folks who were on a 7-8 hour pace. (And the XCM course last weekend didn’t include any of the really technical stuff… 
)
The folks I ride with all cut our teeth riding those trails on 26” hard tails so it kind of becomes second-nature. Michaux SF is a few miles north and it’s even more technical. Up until very recently they ran an amazing race series up there consisting of three 40-mile races throughout the season. Fun stuff!