I think the giant mentioned here is a reference to the Mabinogion, the great
Welsh epic (by inference it can be deduced that both the giant and the dragon
in 'Farmer Giles' come from Wales, the 'mountains to the North and West' of
England). In particular, one character comes to mind: Bran, the giant
king ('too tall for any building to contain') who owned a magic copper cauldron
reminiscent of the giant's copper pot. This cauldron had the property of
returning life to any corpse thrown into it, until it was burst when Bran's
giant half-brother threw himself into it. I don't know if this particular
myth is what Tolkien had in mind; there are plenty of other magic pots and
cauldrons in Celtic mythology. And Bran is not particularly stupid.
I think the intent is simply to give a sort of caricature of the Celtic
mythologies.
painting by Goldilocks Took
