I take it you only read this article because nowhere in the Khronos Press Release or Blog does it say this is 'based on Nvidia extensions.'
It says it provides the same functionality as Nvidia extensions plus extras but that isn't the same thing.
It was on the Khronos blog like a month ago and some Vulkan RT game developers were talking about on some other tech sites, perhaps Beyond3D.
This is not surprising, because nvidia's Vulkan RT extension were a direct copy of the DX12 API, and Vulkan uses the same HLSL shading language as DX12 where the RT specific shading code exists. Vulkan API is trying to stay as close to DX12 as possible.