Author here :)

> a belief by the author of this post that Info-ZIP is the canonical implementation

↑ Where did you get this from?

I don't think nowadays there's such a thing as a canonical implementation — ZIP implementation world is too fragmented and implementations are too widespread.

One more note is that the article isn't about who's right or wrong in terms of interpreting APPNOTE.TXT — this is besides the point. The point there is that a parser discrepancy can cause security issues, and the article documents just another discrepancy found in the real world implementations (and there are A LOT of these with regards to the ZIP format).