Having had a chance to watch Julian play at close range, he plays a regular five string with the fifth removed. It sounds like he tunes DGBD, but I could be wrong.
His strum style is almost like a jazz banjo rhythm, but done without a pick. The one song he played used a familiar progression: first and fourth strings fretted at the 5th, then both down to 4th, to 2nd, then up to 3rd. Try it – it’s fun!