Byron clearly feels bad about killing the bird, but he doesn’t want to show his emotional vulnerability to his little brother. Consequently, he acts mean so that Kenny will go away—a confusing turn of events that makes it hard for Kenny to understand what, exactly, is happening inside his brother’s head. Suffice it to say, what’s happening is that Byron wants to look like a cool, apathetic teenager when, in reality, he’s a caring and sensitive soul deep down.