That is just the runtime (opencl driver) not the whole Software Development Kit, it was a misleading name, on the new download pages it is now called the OpenCL driver.
The SDK would also include the kernel analyzer and other tools and samples. The naming is confusing I know, but you are not getting the SDK as part of the main graphics suite, just the SDK's opencl driver.
It's like DirectX, you can install the SDK 'runtime' which includes what you need to run games programmed using the DirectX SDK, or you can install the actual SDK which is much larger and includes sample libraries and debugging tools.
The 2.1 SDK includes the old driver, which was not included in the main graphics suite at the time.