ford mustang axle question

so it's 2:44 am, I just got home from pulling Tara's car into a parking lot because the rear axle on the right side snapped. The wheel and tire came off and the hub of the rotor shattered. I did just do a break job all the way around. I will post pics in the morning but does any one have any idea on how this could have happened? Did I tighten the lug nuts to tight?