They are essentially the same. The first one stresses that he is my father's friend: he will act friendly towards my father. The second one stresses that my father is his friend: my father will act friendly towards him. Usually, however, the distinction is unimportant.

it is the same, but the second one it's miswritting

Here is an explanation that I like. (Sorry, I forget the source.) 1. A friend of Bill. = friendly feelings toward Bill, but it involves Bill much less. Bill need not even know that this person has friendly feelings toward him. 2. A friend of Bill's. = one selected from among all of Bill's friends. These friends belong, in some sense, to Bill.

To add to Chris's explanation, "a friend of my father's" is equivalent to "my father's friend" or, perhaps more naturally, "one of my father's friends." If you want to read more about it, the construction is called a double genitive. Here's a link: https://www.thoughtco.com/what-is-a-double-genitive-1691017