Wild caught discus can be one of the more difficult species to get eating regular fish food, than most other tropical wild caught fish. I know this because I have wild caught discus. They can be finicky eaters in an aquarium, but in the wild those foods are the best suited for them. The reason they can be picky, is because we always try to feed them foods they don't naturally eat, like beef heart, blood worms etc. Which can be why buying older wc discus can be a difficult task getting them to eat flake and pellet foods. Younger wc discus IME are easier to introduce new foods to, than older ones. Which is one reason I prefer to buy them under 4" in size if wild.
It is very neat to see them in their natural habitat's, and I highly encourage people to keep them in planted tanks rather than not. Especially ones with lots of driftwood as well. Discus can be very sensitive to high nitrates, which is one huge benefit to having lot's of healthy live plants. Just my 2cents