The shell consists of two parts. The other one is painted black inside to block the light from the self-made LED display. The inner one houses all the rest.
To seperate the two, you have to remove two opposite clips by driving sth. between them - these might be toothpicks, but also can be bits like in this case.
When you spread the clips apart, you can slide the other shell off - revealing the self-made LED display and its cover.