In that case, it sounds like it just depends on whether you paste the code directly into an existing file. If you paste the code into its own file, then import it into your project, the distinction seems to vanish.
A library isn't just code that happens to be in a separate file. Someone chose an abstraction layer at which to create a library, wrote the library code, tested it and wrote documentation.
If you went and copy-pasted some code on stack overflow into a file, put it on github and released it as a "library", I might not agree that it was one.
If you went and copy-pasted some code on stack overflow into a file, put it on github and released it as a "library", I might not agree that it was one.