That's not game design, it's UX. They're closely related, though, but completely different "ends". If you're not modifying any game systems, it's _not_ game design.
The "technique" (which is not new, it's basically Material from Android and what they did for the Notification Panels since Lollipop, circa 2014) is decent, but you should use either a button or the user tapping outside of the panel because it goes against current mental models. Maybe in 5 years it might be default.
Look how the old and new Cut The Rope does it, then clone it. Nothing wrong with it.