UAL 777 to EWR

Does anyone know why UAL used a 777 to EWR the morning of March 11th? As you can see, UA98 was operated by a 777 instead of a 757 on the redeye, and then continued on as UA473 to Denver. Does anyone know why a 777 is being used here?

Maybe the 757 went mechanical or it was an overbooked flight.