I usually keep puppies on 3 meals until the 12 week or so mark, If he is phasing it out on his own you can split it into 2 feedings, just increasing the amt am/pm..I find my pups do very well on 3 cups per day total.
My 14 month old still get 3 meals a day. Lunch is a large Kong with his biscuits mixed with yogurt and then frozen. It sounds like your puppy isn't too interested in lunch and you are starting to phase it out. It should be fine to feed the half cup until you think he can do with 2 meals a day.