The angel of God said to him, Take the flesh and the unleavened cakes, and lay them on this rock, and pour out the broth. He did so.
So here was Gideon hiding from the Midianites as he was threshing the wheat because if the Midianites had caught him they'd take the wheat. And so he was out by the winepress threshing wheat and here was an angel sitting under an oak tree.