The article title is straight up misinformation at present. From the article itself:

The FuryGPU is set to be open-sourced. “I am intending on open-sourcing the entire stack (PCB schematic/layout, all the HDL, Windows WDDM drivers, API runtime drivers, and Quake ported to use the API) at some point, but there are a number of legal issues,” Barrie wrote in a Hacker News post on Wednesday. Because he works in a tangentially related vocation, he wants to make sure none of this work would break his work contract or licensing etc.

Nothing against OP who simply copied the title, nor the project author. This is impressive but it’s not yet open source and there may be legal hurdles preventing it from becoming so.