The aircraft would not have survived a -4G push. -1G is the normal airliner design goal for no damage and -1.5 for failure. In addition it’s doubtful to impossible that the airfoil on the 767 would be capable of producing -4 G’s at 210 knots. It’s not a symmetrical aerobatic airfoil and it CL would be very poor under negative G. It would exceed the stalling AOA well before 4 G’s.