So in this case copilot just looks at the situation like that someone gifted me this, and does not question if the person gifting was the real owner of the gift.
If you can figure out a method of determining whether someone owns the code that doesn't involve, "try suing in court for copyright infringement and see if it sticks" then we're kinda stuck. Because just because a codebase contains an exact or similar snippet from another codebase doesn't mean that snippet reaches the threshold of copyrightable work. Or the reverse being that just because two code snippets look wildly different doesn't mean it's not infringement and detecting that automatically is solving the halting problem.
The thing you want for software to actually solve this is chain of custody which we don't have. If you require everyone assume everyone else could be lying or mistaken about infringement then using any open source project for anything becomes legal hot water.
In fact when you upload code to Github you grant them a license to do things like "display it" which you can't do if you don't actually own the copyright or have a license so even before the code is ever slurrped into Copilot the same exact legal situation arises as to wether Github is legally allowed to host the code at all. Can you imagine if when you uploaded code to Github you had to sign a document saying you owned the code and indemnifying Microsoft against any lawsuit alleging infringement o boy people would not enjoy that.