It'z a way to force a physical action to unlock. For all the successful blocking or screen time management apps, the surest way for success is to encourage a physical action or to enforce some sort of time delay so that the person's default motion memory can't robot their way through whatever the block is. If all you have to do is hit "ignore," then in like 2 times the brain can completely move through that "barrier" without any thought or conscious decision. It becomes little more than the same motion as opening the app itself.

The idea of making a physical device to unlock the phone again is pretty clever actually. It's kind of like those alarm clocks that drive around on the floor so you have to chase them to cut it off, lol. I think in the context of what they are trying to do, its actually pretty important and might be the difference between something that is easy to ignore and something that may actually force you to weigh the costs of going back and being distracted on your phone again. At least I'm pretty certain this is the logic behind it