I assume that they mean that OpenCL, which is a traditional GPGPU language, is a very restrictive subset of either C or C++ (both are options) plus some annotations.
In fact, OpenCL toolchains already use the Clang frontend and the LLVM backend, so the experience of using and compiling them is very close to C++.
The talk mentions all of this; it says that a benefit of using full C++ on the GPU over using OpenCL is that you don’t have to deal with all the annoying restrictions and annotations.
What you are looking for is some way to shortcut the process of learning to write an operating system by re-using your existing knowledge of Python.
(I’m not judging that; I understand why you want to do it)
The simple truth is that there is no way to do that. Any solution that involves using Python in a kernel would cost you more in terms of complexity and time than learning C would.
It is rarely worth it to use a language outside of the domains that it is normally used for.