Remy, 5.3 pounds is not a teacup. In fact, no where in the standard does it distinquish teapot...teacup...and so on. Your Yorkie is actually perfectly within the standard of 4-7 pounds.
To the original poster- Your little boy, while out of standard in weight, may just be a bigger Yorkie. If you weren't planning on breeding him or showing him then I'd just love him the way he is.
No need to cut back his food if the vet or staff said nothing about him being obese. And besides, even if he were "fat" he'd still probably be a 8 or 9 pound Yorkie w/ the weight off. He's just a big kid and I'd love to see photos!