Even Trains magazine's own articles get the terms of art incorrectly sometimes. ATC and PTC are different. You can have PTC without ATC. You can have ATC without PTC. You can have both. You can have neither.
PTC is simply a penalty brake application when a rail vehicle exceeds a speed restriction or when the vehicle enters an occupied block without authorization, or when a vehicle passes a signal showing a stop aspect ("signal passed at danger" in the U.K.). Enhanced versions of PTC show positions of trains independent of any signalling or track circuit.
ATC means just that: automatic train control. The train is controlled directly by wayside and onboard equipment to automatically accelerate, decelerate, stop, and start. The article isn't correct. The Washington DC Metro has run on ATC since 1971 but not PTC. It's not perfect. The deadly crash in 2009 temporarily suspended ATC operations until this year, and that was because the signals were not being properly handled during an upgrade.
Magazine editors make mistakes. I wouldn't get too wound up about it.