Luciano Barbera confounding the ‘Rule’ followers with his bottom button done up.
Don’t try this at home, unless, as I suspect here, its a coat that has been cut specifically to fasten at either or both buttons. A configuration made famous in the early 20th Century by the likes of Anthony Eden & the Duke of Windsor. Later, more American styled examples of this 2 by 2, or ‘Paddock’ style coat, can be seen worn by J.F.K.
Of course, Mr Barbera could just have deliberately fastened the wrong button as an example of what has become known as ‘sprezzatura’!