Well, in terms of guitar playing I guess the complexity of what you can do with a guitar is a part of it, and also there's the question of precision. Finally, and here is where objectivity goes out the window, there's the matter of virtuosity.
When comparing the lady in the video with, to use my previous example, Jimmy Page, is that I'm betting she can do everything he can with a guitar, while the opposite is almost certainly not true.
Edit: This a reply to Baley's unedited post.