Neither are that hard to explain plausibly, and the wikipedia page does so. Brain damage could come from concussive forces applied from the blasts of the (speculated) explosive ordnance tests, this would in turn explain the absence of external soft tissue trauma? The tongue part, as is the case for a lot of missing limb story, sounds like some critter found a soft, yummy looking part of the corpse and made away with it.

The bigger mystery IMO, is the absence of reported blast marks or damage to the terrain one would expect from testing explosives.