I've just re-read it, and I really think that the Capulet servants are provoking a fight having seen FROM AFAR the approach of Tybalt, their master's kinsman. They taunt the Montague servants in front of the newly-arrived Benvolio, who they know will get involved in trying to calm things down. The scene is made to show the animosity and bad feeling between the two houses and even between the servants. On stage, Benvolio AND Tybalt can approach one ahead of the other. The servants' exchanges do not take more than a couple of seconds to deliver.