Has he? The ones I'm aware of he was complaining about the low quality of the generic kernel drivers. AMD software had a tendency to crash when doing anything outside of standard video games (which was my experience too, but I've caved and bought Nvidia since then; average driver quality of Nvidia on linux seems to be much lower but the kernel doesn't go down which is nice. Got a lot of OOM errors where on ROCm the kernel froze requiring a full system restart).

But this is interesting and probably strong evidence that the CUDA API isn't the moat people thought it was. CUDA multiplies matricies and that is close to a commodity operation. The moat actually seems to be Nvidia's higher generic software engineering standards, the difficulty in writing job scheduling/memory management infrastructure and possibly the fact that closed firmware is the norm.