Keep calm people. It may be just a rumor.
It isn't a rumor when the author of part of the code clearly says his code has been infringed without due credit.
The author of the code can't know if it was infringed without seeing the source. The authors solver is slower, uses more VRAM, uses a lot more CPU, and PCIe bandwidth, runs on fewer cards, and crashes a lot. Why would you want to copy that?
The author of the code was able to see part of it. Claymore got in a rush to release a linux version and didn't secure the release from partial inspection. That inspection found direct copying of code without permission from the author of that code or credit given under the MIT license.