All developers Copy paste
If you find that strange, you have not coded anything. All code uses libraries so much so that they re usually dynamically bound to facilitate copying code with even having to read it. Statically bound stuff like virus code will use copy paste more. Natch.
If we didn't copy paste and every bit of code ever written was originally we would still be writing binary.
Re: "The malware developer also includes an embedded "Snake" game that is likely directly copied from a GitHub repository and doesn't seem to serve a purpose, another proof point of the irregular sourcing of the code."
I actually did exactly this too. I was writing a mock Nokia mobile phone test utility ofr a wap site we were building (showing my age) and I embedded a copy of Snakneot to it just for laughs, probably cost our qa a few hours ;)