More than likely... he simply forgot he was using it. There are stories of him meeting people on the street earlier in Argentina. He would quickly pull his hand out of his pocket to greet a person with a handshake and the rosary would be attached.
Then he should maybe consider not wearing it.
It would seem to be a pretty important requirement of wearing it properly would be to use it as privately as possible, thereby not coming across as "LOOK WHAT I'M USING", as he is in that picture.
Would it be too much to ask that we adopt a presumption of innocence?