Some thoughts....
The skill level was unquestionable.
I actually thought they looked like they were enjoying themselves rather than in terror of their lives (they let slip a few grins when they start slapping, no doubt because they know its unexpected). Playing it properly was no more than a lot of other musicians do.
There is a limited range of music in North Korea although there are supposed to be a tiny handful of metal bands. Most pop music is pretty gentle and has its roots in folk music. No doubt the classic hit "The Joy of Bumper Harvest Overflows Amidst the Song of Mechanisation" is unlikely to pwm iTunes in the near future.
This combination of modern music against a traditional backdrop appears a fairly typical approach. The use of a relatively unobtrusive (but no doubt familiar to the audience) piece of background music is probably a good idea for an exhibition piece, but if a bit sterile if you were going to hear 90 minutes of it.
Most importantly it shows an obvious idea that doesn't seem to have been given serious consideration before.
As bass players we all know bass can be just as complex and demanding as guitar, but in a typical band situation the higher pitched, vocal like, sounds of the guitar is more suited to solos. But a true solo guitar? You get something like Eruption - I've seen a video of Eruption live, eh beginning was electrifying but I couldn't watch it to its long, drawn-out ending.
In contrast a pair of bass guitars, because of the added element of more solid tones and wider harmony gives something potentially rather more engaging.