Hey it looked like you were using the fill brush with gradient two times in a row at 11:35.
But whenever i try to do that it just deletes the first fill and replaces it with the secound.
Hey ppanophobia , it looks like it's replacing it for me as well. The second and third stroke are not adding anything, but rather tweaking the placement of the start and end of the gradient. That said, you can lower the Alpha in the color wheel to not have it replace if you don't want it to. Hope that clears things up!