This was no accident, or in the unlikely event that it was, then it shows what happens when cronies rather than professionals serve in protocol positions.
Was it deliberate, the most likely possibility? Then what was the message, and for whom? My immediate thoughts are that this may have been a message to a set of foreign observers, of the diplomatic kind, meant to separate the speaker from his message.
A most remarkable thing, indeed, in any case.
Supposing that this was a deliberate signal, I'd be interested in other's immediate thoughts on what it was meant to communicate and to whom?
For example, did the anti-president think he was going to get questions about his endorsement of the remarks made by Calderon?
My guess is that his staff hastily threw the press conference together, and being the good Marxists they are, completely forgot about the flag.