the reason for this is that the gravity already starts to affect the box while the splash screen is displayed. So until it is finished, the box has already fallen down. As soon as you add the ground wall, you will see the box stays on it after the splash finished. We’ll update this tutorial to only start falling after the splash is finished (and will update the z property), thanks for bringing this up!
If you have any other questions about the tutorials or the sample games, just let us know here in the forums.