I found an "os.path.join" in the first .ipynb I looked at. It seems to construct a path that is relative to the working directory, not to a data directory.
As a side note, pointing folks at a whole GitHub repo instead of putting the relevant code into your posting is not exactly reader friendly. Even less so when the code is only a fraction of an .ipynb file in JSON format, which must be looked at in raw format because GitHub cannot render it.
cheers,
Roland