See for yourself. Download the Heaven DX11 Benchmark. Run it in DX11 API mode and then OpenGL mode and see the difference. There is a difference, but it's fairly minor. Usually DX11 or OpenGL will be the first to support a new feature, then the other supports it in the next release. The end result is that they normally produce a similar graphics quality.
I don't think that the summary is racist at all. Making a conjecture that a Chinese IT company, owned by an Ex-Chinese military officer, is purposefully leaving vulnerabilities in it's products that the Chinese government can exploit is sensational, but not racist.
Takeaway: the linux kernel and OpenGL are arguably more efficient than their Windows-based counterparts. I think a lot of people have thought this to be true for years, but it's always nice to see solid comparisons. It's a good time to have a linux box!