How does the homeless man save Sal in Chapter 45?

In Chapter 45, Miranda is walking home when she sees Sal ahead of her. Marcus comes out of his building and calls to Sal. In a panic, Sal runs. Marcus sees that Sal is about to run in front of a truck and tries to stop him, but cannot catch him. The homeless man, however, is at the right place at the right time and is able to kick Sal out of the way just in time.