Without knowing the circumstances, my guess is that the operator in question had a close shave when a steering pin was either not fitted or malfunctioned, and the steering hydraulics became pressurised. So the SOP was probably changed to ensure the steering hydraulics remained unpressurised until the push crew had removed the tow-bar.
At one time we used to switch the nose-wheel steering off during pushback (Airbus), but in later years we we left it on, I think there was a software update.