What's funny is that apparently there is a giant blacksmith who builds and sells giant axes to his customers
Given its crude design, I could imagine it as being little more than a semi-dull, re-purposed bit of iron or steel plate. Maybe even given to him for use as a mercenary in an army of orcs, ogres, or even humans.
Given that other recent posts on the fantasy forum also showcase airships, sentient (?) mushrooms, frogs with tits, and what appears to be a Bosch painting recreated in miniatures, I wouldn't blink twice at an oversized axe.