The way I see copilot's output is that it's already in the grey zone. As with other models like this there are no snippets in the model. I can for example generate similar looking code to the cs_transpose function in Lua if I nudge it a bit. To me this seems equivalent of someone remembering exactly how a function works (to some extent..) and being able to write it in whatever language without copy pasting.
So the output as far as I understand is very grey. Maybe there's something in the training part that can be discussed, but as I mentioned earlier I'm not sure what else you can do other than check the license of some code or avoid creating copilot in the first place.