Were they solid body guitars? How did the pickups work in these 9th century guitars? Can you show me one with cutaways like this one? That kinda of tailpiece? Bridge? Tuning pegs?
Seriously, I think it is a pretty cool anachronistic piece. I like it. But if the defense is that it isn't anachronistic and actually fitting to the time then you are slapping the artist in the face. Because if the artists intended the viewer to see that and think 10th century guitar, then the artist failed spectacularly. If, in the other hand, the idea is that in a world with magical music a guitar might look a lot like a modern electric, then he did a very good job.