What are the 'natural flavors' in a fruit drink that contains no juice?
Ok... I'm going to ruin your day with this.  In orange juice for instance, the process of homaginization and storage kills the flavor of orange juice, so the industry has enlisted the help of the perfume industry to help them.  Each orange juice company has basically a perfume of orange flavors that it uses from the peels and rinds and biproducts that it uses to try to recreate the taste of real orange juice... It's why every orange juice brand tastes slightly different even though they are all "fresh squeezed" (btw, they are technically fresh squeezed, they're just then stored :))

If you google "orange juice flavor packs" you can see what this is talking about.  The flavor packs are incidentally made out of parts of the orange, so the fda has no problem with them (sadly).

http://consumerist.com/2011/07/oj-flavor-packs.html

So to directly answer your question, you can flavor something with fruit derived perfume and call it "natural flavors"

Here's a quote from the site:


  Juice companies therefore hire flavor and fragrance companies, the same ones that formulate perfumes for Dior and Calvin Klein, to engineer flavor packs to add back to the juice to make it taste fresh. Flavor packs aren't listed as an ingredient on the label because technically they are derived from orange essence and oil. Yet those in the industry will tell you that the flavor packs, whether made for reconstituted or pasteurized orange juice, resemble nothing found in nature. The packs added to juice earmarked for the North American market tend to contain high amounts of ethyl butyrate, a chemical in the fragrance of fresh squeezed orange juice that, juice companies have discovered, Americans favor.