Yes, I misinterpreted the article. Here's a clearer description from spaceflightnow.com (https://spaceflightnow.com/2016/09/23/falcon-9-rocket-explosion-traced-

Yes, I misinterpreted the article. Here's a clearer description from spaceflightnow.com (https://spaceflightnow.com/2016/09/23/falcon-9-rocket-explosion-traced-to-upper-stage-helium-system/ https://spaceflightnow.com/2016/09/23/falcon-9-rocket-explos...): "The Falcon 9 rocket’s upper stage liquid oxygen tank contains several composite helium vessels, each pressurized to about 5,500 pounds per square inch in flight. The helium is routed through the second stage’s Merlin engine, where the helium warms up and is injected into the rocket’s propellant tanks to pressurize the stage as the launcher burns fuel, keeping the tanks structurally sound."