This is init-ing an empty repo at `path`, but at [L57 here](https://github.com/olmobrutall/libgit2sharp/blob/362f6242da94363cd2802096a396b1502c8ef67d/LibGit2Sharp/SubmoduleCollection.cs#L57), you're attempting to clone into that directory.  In order to clone into a directory, it must be empty.