Like most people, I'm pretty surprised by the chosen finalists. They set up judging criteria, but in the end the criteria is so vague and open to interpretation that they can really justify any position they end up taking. Without any transparency or actual scoring, it just comes down to gut feelings. The written criteria for this contest was: (i) authenticity; (ii) technique; (iii) style; and (iv) presence. You can see that these are just general terms that are completely open to interpretation. To be fair, music isn't something that fits neatly into some objective criteria and the bottom line is that people hear music differently.
I read a blog with a quote from Joe saying “Each of these ten finalists impressed me not only with their technical skills but how they were able to showcase their personal musical styles in the songs...” I'm not sure how legit this quote is, but it sounds like it came down to style. Listening to the finalists, I wasn't really impressed with the technical level of the players and I'm not really even talking about the typical speed and precision aspects that typically get associated with it...I'm just talking about having command of the instrument. Playing in tune when bending or using a slide...that is basic musical technique in my opinion.
As far as the style comment, I think it's fair to say that most of the players showcased their personal musical styles. What they are really saying is, they preferred these styles to the styles of other contestants. I was surprised that Dust Bowl, which seemed pretty popular, wasn't represented in the top 10...but Slow Train, which didn't seem to be a very popular song among contestants, took 2 spots. This was probably indicative of the stylistic preferences on the judging panel...Whale, Slow Train, Stone Quarry represent 7 of the spots.
Good luck to the finalists!