Well, shock of shocks, the article was imprecisely written.
Any US citizen anywhere in the world can vote, assuming s/he got a proper ballot and sent it in on time. My daughter voted from Japan and from England when she lived abroad at the time of US elections.
Neither did Alaska and Hawaii before they became states. Consequently, their residents couldn't vote in a federal election either.
A citizen who claims residence in a territory cannot vote in a federal election. A citizen who claims residence in a state may vote from anywhere in the world.