This was of course a way of making fun of Germans, never too popular in the Italian Peninsula at the time (and even less popular after the two World Wars, trust me).
So it was the idea of the flamboyant German costume that was teased. Is the stick in his hand a reminder of the Plague Doctor? Who knows.
But there is more to it, because at the time Venice had quite a big trading business with Germans which was quite strong in 1314.
There were so many Germans in Venice all the time that they were relegated - to make sure they would pay the due taxes, and not try to do business with others except the Venetian authorithy - in a building expecially made for them in 1228: Il Fondaco dei Tedeschi (Factory of the Germans).
The building would be locked up at a certain time at night, being patrolled by Police on the outside and with spyes roaming the inside.
This made the German community bond because of the segregation, but since they were making good money this way, they had to bear with it: business is business, after all.
