Yeah, except for the fact that if he were in Canada, he could be forced to comply with their law. If they called up men for the draft, he could be called and he could be forced to serve.
Do you imagine they could do such a thing to someone born in the United States to Citizen parents?
It's not theoretical either. Men born on English Soil of French Parents were executed for Treason because they wouldn't fight against France.
Be sure to mention that risk when pitching your view of the NBC clause to voters and to their electors. And, don't you understate the likelihood of that risk when you tell them! ;-)