Milling is cutting into smaller pieces. Salting is adding salt. Two different things. Typical cut size is 1/2" by 1-2". I guess you could do it by hand but a properly cheddared curd is rather firm and doesn't break up all that easily. It would be time-consuming. At home, it's easier to use a knife and cut the curd slabs.
Key is to have same-sized pieces so salt is absorbed evenly.