Okay, I think this is a bug but I am not sure. Weather ogres I believe at one point, did nature damage with the majority of their attacks. However, they are doing energy damage with everything besides Ogre's Cry which is mind (and I don't believe that is wrong). Thundering Blow, regular attacks and such should be doing nature damage I thought. So I think this is a bug (much like the fire pygmies and such doing ice damage instead of flame, but that was fixed).