Where American exceptionalism comes in is the widespread belief among American that their country does not act in the world stage in its own national interests - that it acts to defend universal human ideals.
How widespread is this belief? I wonder. It's complicated because in many cases, the two are not mutually exclusive. IOW, to act on the world stage in defense of universal human ideals is often in the best interests of the US.
Now, whether or not we defend those ideals, or achieve them, is an argument worthy of far more effort than a thread on a forum - it's the overriding question of the day.
However, because those two things coincide but work against the self interest of other players on the world stage does not negate the coincidence of those two things.