Is that your opinion as a professional historian?
No, it’s my opinion as a former protocol officer.
I am an historian and currently work as a history teacher. But this is not really drawing from my general historical knowledge, but rather from knowledge of current diplomatic protocol.
Pope Francis was, in my view, doing nothing other than being polite - more polite than he needed to be, but there is nothing to say a gentleman should only do the bare minimum than is required to.
This is no more a violation of protocol, than Ronald Reagan bowing to Queen Elizabeth was.