If it's like XI then it works like this.

You only need 1 code for your account however you need 2 copies if you want to play on ps4 and pc because you still have to download them seperately.

Basically I think it means this:
you can borrow a person's PC version to download the game and use the ps4 code to register the expansion and you are good to go.

At least if I recall correctly that's how it worked in XI