Act II, Scene I: At the party why does Claudio pretend to be Benedick when approached by Don John?

Don John and Borachio figure out who Claudio is by his bearing. Don John approaches him and asks him if he is Benedick, and Claudio plays along, claiming he is. Don John tells Claudio that he should separate Don Pedro and Hero because she is not equal to his brother's birth. Borachio chimes in as well, telling Claudio that he heard Don Pedro swear his affection for Hero and plan to marry her that very night. This will set up the scandal meant to dishonor Hero.