When the air-raid siren goes off, the singing is over and Binghamton comes to the side of stage to talk with McHale. In the background you can see Rosa singing away, but when Binghamton goes back out she is just standing on stage listening to siren with others.
Rosa tries to to butter up Binghamton by confusing his record with "Mario Lanza". Mario Lanza was not a famous singer until 1949.