In their partial defense, I'm not all that sure anyone in the AVG had ever seen a picture of an A6M Zero. From what I heard it was all just verbal description along with some "preliminary" blacked out 3-views. That is, of course, second-hand information. But the blacked-out 3 views even in the TAIC manuals weren't all that good some 5 years later.
Perhaps they thought they were fighting Zeros from the vantage of an honest mistake. I don't really know.
I think part of the confusion is that Chennault certainly knew all about the Zero and was doing his best to warn the US about how advanced Japanese aircraft were - as the CIA documented.
https://www.cia.gov/library/center-...-Chennault and Intelligence-v2-with Notes.pdf
Interesting document, seems to indicate Chennault was the "godfather" of Air America!