The whole series is heavily steeped in norse mythology (including, uh, the main character's surname), as well as a hodgepodge of other eastern mythological/spiritual ideas, so it really doesn't seem like a huge step to name a hammer after something in the 'human' world. After all, isn't that what they're trying to do with the whole series, show that our common mythology is based on common experiences? Remember the car hood ornament in Tarabon? Remember the story of "Lenn" who went to the moon or whatever? You can roll your eyes justifiably, of course, but I don't think it should be a surprise at this point.