He is misinformed. Any dog who's nails are kept longer could be in pain while getting them clipped. As the nail grows, the quick (blood vessel inside the nail) will grow longer into the tip of the nail. If they are kept shorter, the quick will recede into the nail and cause little problem. I recommend nail grinding. This will cause little pressure on the nail and decrease the amount of pain the dog is in. The nails should be short enough that the are a couple millimeters above the ground when the foot bears the dog's full weight.