Nobody said anything about the Roku app. You don't need the Roku app for anything. Well, it can be used as a remote for the Roku, but it's certainly not needed. I never said anything about the Roku app. I don't know where you got that from.
Open the Netflix app on your phone. Cast to Roku. Netflix plays on Roku. Then turn off the phone while it's playing. Netflix continues playing. Because it's playing from the Roku app.
Again, do what I said to test. And you'll learn something.
You specifically said "maybe the roku app is playing?".
