The magic of how to drive 7 LEDs with just 2 GPIO is shown on the right in the schematics. Please see here for a detailed description.
PB1, the remaining free IO pin, is used for the touch button.
The entire board is about the size of a real die. (which I did not have for size comparison, but the coins should do).
i made a slightly different version of this board. 15mmx15mm pcb with same schematic. I can share kicad and gerber files if anyone interesting. Really good job Tim