Even if you were watching them, you don’t know that they don’t have an app that plays a game frame at 1 Hz that they sync their minds to while you see the other

Even if you were watching them, you don’t know that they don’t have an app that plays a game frame at 1 Hz that they sync their minds to while you see the other 59 frames at 60 Hz and think you’re seeing a book. Without root access to the device and blinkers to ensure they aren’t looking at a second device strategically placed out of sight, you can’t conclude anything.