Dan laughed right when the guy said the little slave girl fell off the roof and died. He knew he had to start explaining what happened fast because that sounded and looked so bad. Especially after saying you have empathy and are sad about dead kids from yesterday. Based on the mentality of the house she was probably pushed by the psychopaths who owned and tortured slaves.
He is right about not discussing shootings on the show in detail because they have never even mentioned Dylan Roof's hate crime murder shooting spree.