Also, when my phone is in my pocket I'm exposed to 50% of the radiation in one small spot vs. let's say 10% of the antenna's radiation spread across the whole body of the rat. Hopefully they tuned the power in their experiment to account for that.
No, when they talk about watts per kilogram I am pretty sure that they mean these were absorbed. Like they literally built 21 big microwaves, 7 for mice and 14 for rats, and then turned them on: it's no different than your microwave at home, the waves bounce around the walls until they find some water to call home. They're presumably not concerned with any microwaves that escaped the resonator.