Most songs run off of a mathematical progression - 1 : 4 : 5. If you take a song in the chord of C, the following chord will be F, followed by C, followed by G. You can switch it around to 1 : 4 : 5, but the old adage of "Three chords and the truth" holds true for just about any country song.
But listen to this:
The chords there are Em, B7, D and A for the chorus. The verses are C, G, D and Am, then C, G, Am and B7.
It's not just blowing the 1. 5. 4 progression out of the water, you have a Minor chord progression followed by C major on the verse leading up to a Minor chord for the transition.
For those who don't speak music, this blows all modern pop music our of the water. Pop music is "C-A-T spells CAT" and what the Steelddrivers are doing is the Illiad.
I'd just like to point out that bluegrass is the heritage of Celtic music, brought to his country by the Scots and Irish who ended up settling in the Appalachian Mountains. Coincidently, this is also where moonshining comes from. Try telling an Irishman that he can't have his liquor, and see what happens.