'Shield' PCB for Arduino/AT tiny85

[Nick]

... (Not sure why it had double pin headers)...

Shields are often designed to stack in a "towering inferno" style. The double row of holes is probably for a row of pins to connect to the board below (probably an Arduino) and a row of sockets to provide test points and breakout signals - he probably meant for those to be there as that's how you use Arduinos