He mentions this under "Caveats": 'There are several limitations to this assessment since the Hooktheory API wasn’t really intended for this type of analysis.

He mentions this under "Caveats": 'There are several limitations to this assessment since the Hooktheory API wasn’t really intended for this type of analysis. For example, it doesn’t mention whether “6” is “vi” (minor) or “VI” (major), which is kind of a big deal.'