If you have a 15" MacBook Pro (Late 2016), then it does have the dedicated Radeon 460 GPU and will switch automatically between the Radeon GPU and the Intel graphics, which is also present since it's part of the CPU.
I think "About this Mac" only shows the device that is currently active, depending on which apps you're running and how GPU-demanding they are. At least that's how it used to be with graphics switching on the older models - can't say for sure since I have a 13" MBP now without the dedicated GPU.
In any case, launching System Information and going to Graphics/Displays will show you all that's installed, including the dedicated Radeon GPU even if it's not currently in use.