Ron Paul is a non-interventionist. He still favors international trade and international diplomacy. That isn't the same as "withdrawing from the world," and certainly isn't isolationism.
Yeah, but "withdrawing from the world" makes a much better soundbite than "noninterventionist" when on the attack.
After all, most Americans would probably agree with a "noninternventionist" foreign policy but disagree with "withdrawing from the world."
It's all in how you frame the debate.