Is my private repo can be scanned for plagiarism purpose through any of the API or Software?

I know this question sounds stupid, but I have heard that the software exist which can scan my source code and compare with existing one (i.e local machine code). I am not sharing here my .git file with project, only sharing the code downloaded with github as ZIP format.

So, Is there any way someone(third person) can compare both local code and my private repo code through any API or Software?

Thanks in Advance!!