Ingvarsdóttir said that the team were able to squeeze a lot of power out of Sony's black box due to being more familiar with the hardware. Specifically, working with Battlefield 4, which was a launch title for PS4, helped the studio acquaint itself with the various intricacies of the machine---and it's quite clearly paid off.
We heard this same thing from Naughty Dog who said that working on The Last of Us Remastered got them accustomed to the PS4 hardware, and helped them make Uncharted 4 even better.
It's always nice to see that even major developers need practice as well. New hardware and software is hard whether you are going solo or have a 100+ person team.