In the Vuelta he won a stage and was off the front on the final climb, most of which he rode out of the saddle. The long standing rule of climbing has always been to stay in the saddle, hands on top of the bars and conserve every bit of energy possible.
But Horner's style of using a few more gear inches and getting on top of them with some weight has served him well. A friend of mine used to copy that and could shed chasers like crazy. He'd get out of the saddle and people would treat it like an attack and use some fuel to catch his wheel, then relax thinking they'd reeled him in. But, he'd stay up and keep churning that bigger gear as he dropped them one by one.
I was never a good climber, but I'm a big guy and that technique helped me. Sadly, I learned it too late.