According to many, many books and articles on the battle, that is partly true.
When Lee invaded the North, his Army marched, the whole way.
And invade the North they did. Lee's invasion caught Washington DC by surprise and sent panic into the North (up until this time almost all of the major Civil War battles had been fought in the South).
They needed more than shoes also, they needed supplies of every kind.
They also needed other clothing, food, water, and other supplies (strategy is fun in the map room, but Logistics wins battles).
Shoes wear out when you march hundreds and hundreds of miles in them across rough terrain:
There was not a shoe factory in Gettysburg though. It was probably the road system that brought the armies into Gettysburg.
Look at this from an eyewitness account: