Disabling exceptions means that you can't catch them, not that you can't throw them.* If an exception would be thrown under such circumstances, the process aborts. This would have been a safer default than undefined behavior (though inconsistent with other fundamental and standard C++ APIs, which generally prefer for the obvious default to be fast rather than safe).

* This is technically wrong, because, e.g., destructors don't run on the way out; I'm going for pithiness here rather than strict accuracy.