sorry, i shiuld have incldued more info.I'm confused. If they put on faster rolling tires, presumably they were LESS grippy, unless the compound was much sticker and they went to low pressure tubeless into the bargain. But you don't mention any of that.
the tires they put in were less grippy. These less grippy, lighter weight tires, which have lower rolling resistance (in the lab and in the flat section), actully took more power (measured on the bike) to climb up the steep, loose, rocky climbing section of the test loop.