(A few hundred amps isn't a lot for a shorted battery, but these are tiny cells so that's what you'll get.)
Two cells was probably selected for one of: Voltage to avoid boost converters, capacity to avoid having to do extensive power optimization to make it run the whole event, balance to make it hang even off your neck.
It's likely not voltage because they're connected in parallel.
A board with a few bits and bobs on and a single 18650 cell might only last, say, 8 hours on a charge.
Now, a well optimized board with a low-power ESP32 and proper use of sleep states would make that number go from 8 hours to over a week, but that does take a lot of extra effort and may not be worth it over just slapping on another cell.
Depending on how bright the backlight was, that could eat through battery. And if they were using the wifi for any active communication, that increases power too.
I suspect they wanted it to last the entire weekend with the display always on. The original design probably only had one cell (maybe even smaller battery with built-in protection) and they hurriedly switched to two 18650 cells at the last moment.
They probably went with parallel because that seemed easier, no need to switch to another voltage regulator and charge controller.