I can understand how you get to your question/conclusion. Again, I would say that being familiar with how Rome answers questions solves the problem, and if one is not familiar with it, how questions arise. Remember, while the answer is not a private missive (that is, the public has access to it easily), it is not an answer to the public; it is an answer to those who have been trained far, far beyond the average person in the pew. And they certainly understand how Rome operates.
I will most gladly concede that Arinze could have been more precise. I hate to say it this way, but it is a little like being inside a club or organization; those inside understand the protocol; those outside do not necessarily understand it, and upon viewing an exchange, can take the answer for more (or less) than was intended by the parties. Cardinal George (and Archbishop Chaput, who was bringing up the question in another meeting) both understood how Rome responds; neither of them have taken the answer to be anything except a response specifically to the question asked (posture at Communion); neither have applied the answer as some sort of “personal choice” to other areas of #43. They are professionals and have dealt with Rome for decades. Arinze gave an answer to professionals which they understood. It is people outside the professional circle who sometimes do not understand the protocols and assumptions at work. They both understand (and so does Arinze) that if Rome intended to modify all of #43, Rome (Arinze) would have said so. They intended a specific question; he intended a specific answer. To an outsider, the appearance is that the answer was much broader.
They knew that he intended to answer their specific question. It would be extremely unusual for Rome to get into other issues without specifically delineating them, and Arinze did not say, “Oh, by the way, this applies not just to Communion posture, but also re-writes the specifics of the Agnus Dei.”
He could have done better, we can all concede. But he wasn’t speaking to the laity, he was speaking to (for lack of a better term) professionals who understood how answers from Rome work.