According to C.J Chivers' The Gun (which is a history of the AK and its impact essentially) it was a bit of both. Kalashnikov certainly had some important input on the design but other members of his design team contibuted/refined some of the AK-47's more notable features (I forgot who is thought to have done what but I could dig it if you really want?).

Another element was the procurement process that resulted in the AK being adopted meant that Kalashnikov and other contributing design bureaus were basically expected to borrow from each other. So there was a first phase of demonstrations, and all groups were sent back to further refine their designs. Since the state's objective was to get the best design rather than to protect intellectual property, it was perfectly understood that designers could/should take the best ideas from each other in their subsequent design.

Semi-related is the probable foreign influences on the AK's design. Kalashnikov is noted to have access to an arsenal with examples of a whole bunch of foreign weapons. As I recall the Garand rifle was noted as a lesser known influence on the AK's design. Hugo Schmeisser, a German gun designer who worked on the Wehrmacht's own assault rifles, was captured and put to work by the Soviets. Exactly how much of a contibution Schmeisser and the StG-44 had to the AK is a bit hard to pinpoint. For example the AK does resemble the StG, but their internals are not that similar. Chivers leaves it undetermined but other authors seem to have been happy to place Schmeisser at the heart of the AK's development.