That's an Arduino uno and three stepper motors sitting at the print head - that thing's going to be really, really heavy. I wonder why he went that route instead of bowden?

At a guess, I'd say he's using the railroad-switching method where the three separate filaments are fed at an angle into the same channel. You need to overcome a lot of friction with that approach, which is probably why the stepper motors are where they are (although putting the Arduino there is a bit odd).

I messed around with a design that used a stepper and a single hot end to switch between filaments, but had a fundamental problem with retraction leaving strings in the filament path that caused too many blockages. I think these two approaches are basically dead ends and we'll all end up using something more like the diamond hot end, with multiple feeds at an angle down into a common melting chamber.