This is inaccurate in a number of ways. Certain American laws are, on their face, restricted in territorial applicability (others are explicitly not, others are neither explicitly limited nor explicitly unlimited and the application requires reference to principles beyond the individual law in question), and, particularly, certain protections of the Constitution have been held unenforceable against the government in the context of certain actions outside the territory of the United States.

But you can't correctly make a blanket statement that US law is not applicable outside of US territory.