Dog becoming picky?

We were feeding our 8 month old puppy his dry kibble 1/2 cup three times a day until recently (about 10 days ago) when he hit 30 pounds. Then the food bag instructed to go with 2 cups for the day. So we started feeding him 1 cup twice a day instead. A few days ago I noticed he started to kind of reject some of his food and not eat all of it so I added a meal topper to it now and feed him less than 1 cup each serving. He has not been lethargic and is active and not vomiting. I think he is just becoming bored of his food Should I be concerned though?