His arm changed the way of the ball. Accident clearly but thats how it is. Gaining possession, gaining control is the same. The "/" I guess means or here.
Laporte did not gain possession (or control) of the ball. Everything else is irrelevant because this did not happen. Even if we accept that City / Jesus did gain possession after the ball hit Laporte's hand, which we do, does not change the fact that Laporte did not gain possession of the ball. Therefore no offence was committed. Therefore it was a goal.
Personally, I blame the English teachers.