Don't read too much into the fact that it appears to show AMM demonstrating hygenic behaviour. They chose AMM as the subject of their tests simply because they wanted a bee of known bloodline. If they had used a hybrid it would have added a layer of complexity to the study that choosing a "plain vanilla" bee avoided. It does not mean AMM shows more or less hygenic behaviour than any other variety. It is the only one they are working with.
However it is interesting to me to know just how hygienic AMM can be as having read Tabers Super Bees and heard him speak, far lower figures can and do appear in Italian lines. sorry I am wrong it is not mentioned in the book so from memory it must have been articles in BKQ.