I can't extrapolate too much from that N=1, but I also wondered if familiarity with the terrain meant something as well. Because the race in question was on Mt. Diablo, which the trail runner knew like the back of his hand. There's something to be said for being familiar with a trail; your body just knows when it needs to gear up for a climb and how nasty it'll be and when it can relax. It's for that reason I was so interested in this great piece by Tommy Rivs about his experience trail racing in Costa Rica. Long story short (but still worth reading the long version), an outstanding college runner got his ass handed to him in a mountain race in Costa Rica by the locals - even after training for it for 6 months. So of course he wanted to know why, dammit. And the answer was that the guys who beat him were porters. Almost every day during the year, they hiked up that specific mountain, with weight, and then ran back down. Not surprisingly, after becoming a porter with them for a few months, he took 30 minutes off his time in a 20-mile race.
Legally you have to put pictures on blog posts. Above, Mt. Diablo from Mt. Tam (from Wiki), below, looking back down Cerro Chirripó in Costa Rica, from summitpost.org.
Perhaps also relevant: these porter guys were porters as moonlighters (literally; read the piece). During the day they worked in coffee fields. So no part of any of their jobs involved sitting down.