Performing with this band seems like a very smart move to me. It is an established band that Matt has worked with before. Because they are local and doing their own thing too, it cost far less to have them perform with him as compared to putting together a new band. Another bonus is that the band has its own fans in the area, so it adds even more excitement for the concert. And Matt performing with a band means he can get up from the piano some of the time, work the stage, dance around, and have a bigger sound!
I'm guessing they are joining Matt in Scottsdale as a dry run for the concert. I hope this all works out, and they schedule some more appearances soon.