IANAL, but unlike patents, copyright violation only occurs if you actually copy the work - independent creations are not infringing, even if similar. While the standard for showing that the work was actually copied is usually not high, especially since these are usually civil suits, some link in a random Google Drive might not be enough.

I'd guess that standard would be set by a court case, unless there already has been one like this (in which case please enlighten me). In general, with vagueness like this, a court usually has the final say.