Electronic clocks do not require that size board. It is not a clock, though there may be a clock circuit on it as well as a clock display output.
Probably has some switching outputs that can switch several relays, and a built in wireless communication function, with both transmit and receive.
It was a setup, and made to look like an IED trigger.
The main point is that the kid did not create the circuit board. It was something pre-made.
I suppose that it could be a microcontroler board which can be tasked to do various things via interface and software, but he did not make the guts.