[Sir Kohran]

The reference to giants goes like this:

When he peeped out in the lightning-flashes, he saw that across the valley the stone-giants were out, and were hurling rocks at one another for a game, and catching then, and tossing them down into the darkness where they smashed among the trees far below, or splintered into little bits with a bang. Then came a wind and a rain, and the wind whipped the rain and the hail about in every direction, so that an overhanging rock was no protection at all. Soon they were getting drenched and their ponies were standing with their heads down and their tails between their legs, and some of them were whinnying with fright. They could hear the giants guffawing and shouting all over the mountainsides.
"This won't do at all!" said Thorin. "If we don't get blown off, or drowned, or struck by lightning, we shall be picked up by some giant and kicked sky-high for a football."
"Well, if you know of anywhere better, take us there!" said Gandalf, who was feeling very grumpy, and was far from happy about the giants himself.

This all just sounds too real to be a 'metaphor'. We hear about them shouting and even playing a game, and Thorin and Gandalf also talk about them. I think they're another 'oddity' from TH that, like the 'wild Were-worms', didn't quite fit in with the Legendarium.