If you can return a XP kick for 1 pt, you can give away 1 pt with a safety.
If you return it all the way, it's two points, not one.
There is actually a way for a team to finish a game with one point, but it's virtually impossible. Let's pretend the KSU player on that play would have ran it back 95 yards inside Oregon's five. Then, he got tackled and fumbled. Then, Oregon picked it up OUTSIDE their end zone, ran into their own end zone, and got tackled. It'd be one point for Kansas State. So a team can finish with one point (but not win the game with one point, because the opponent would have had to score a TD for that to happen).