Hi Will, assuming you flat-tow the Taurus, it's highly unlikely that anything from towing could/would have damaged system by itself.
Here is a good tech article on diagnosing EPAS systems.You don't mention if you got any codes or symptoms that caused you to bring the car to the dealer. The article does point out that damaged suspension components will cause the EPAS to throw a code, and that damaged bellows on the steering rack that let dirt/moisture in also affect system performance.
Similar to how old-fashioned power steering works, the rack is free to move on its own, but no assistance is provided unless called for, and without power to the unit it won't attempt to assist. Is it possible there is power to the EPAS unit when being flat-towed so it's trying to provide assistance?
What did the dealer say was wrong with the unit when they replaced it?
