Why is Budai often associated with the future Buddha Maitreya?

Many times I've heard of Budai (pictured below) being associated with Maitreya, the future Buddha. Why is this so and how widespread is this belief? Wikipedia lists a short verse uttered before Budai's death: >Maitreya, the true Maitreya has billions of incarnations. Often he is shown to people at the time; other times they do not recognize him. Is there more to this association or was the simple utterance of that verse so long ago the sole reason for believing that Budai was the bodhisatta?