That is really impressive!
I didn’t join this challenge because I knew I had to train for long distances on flat, and ended up doing half the ascent targetted by those guys.
Here is a good summary of the event, which includes hours riding time.
I think the results from the event was quite dependent on time available as much as hill climbing ability.
Speaking for myself, I had an advantage because I had hills in the streets of my neighbourhood that I could ride to and hill climb.