I don't think they are using an Arduino Mega. They are using the same processor that an Arduino uses which is the Atmel ATmega, which is a very common processor for microcontrollers.
I'm guessing you're not accustomed to the arduino parlance. Everyone knows arduino uses an atmel atmega uC, but when you say "arduino mega" it means something specific. I have around 5 different models of atmega chips at home that I use with the arduino.
In the video they said they were using a mega, and you can tell from the picture that the atmel chip is a surface mount similar to the 2560. All the arduino chips use some kind of atmega variant, but the arduino mega refers to the atmega1280 or the atmega2560. The most common arduino chip is the atmega328p.
The atmega series is fairly broad. The arduinos only use a subset of the atmega series. "mega" is probably a bit confusing, but if you say "arduino mega" it only refers to one or two specific chips -- the old "arduino mega" used the atmega1280 while the newer model uses the atmega2560.
