It's not false. Have a read through of Valve's presentation of Vulkan at GDC, hosted
here on the Khronus site:
"Mantle pioneered & led the way" page 8
"Based on Mantle" page 10
Nvidia has two methods of providing features that run to the benefit of their cards. CUDA based enhancements that can only run on Nvidia hardware as this runs on their own platform and API such as GPU PhysX and features that run through DirectX but using their libraries. The first is a legitimate competitive practice - Nvidia has spent R&D creating these features and they have every right to have these run on only on their hardware. The second however is very different. There is no need for a developer to use the latter as they do not add any functionality that requires additional code to be implemented, they are simply features available in DX11. AC Unity is a prime example; the Gameworks features are part of the DX11 spec but use Nvidia's libraries (putting Nvidia at the front of a feature name does not make it something they invented, they are all part of the DX11 spec). In these instances these libraries essentially act as middleware tailored for Nvidia cards. This is damaging to competition as it provides an artificial advantage for Nvidia hardware as it is attempting to close off access to what has always been intended to be open for the benefit of fair competition. Making situations like this comes under anti-competitive practice. Microsoft was beaten in court for doing less (bundling IE in Windows).
You might not understand the idea of what DirectX is supposed to provide and may be too young to remember the era before DirectX became dominant, however this is what it was designed to avoid.