Pat Metheney is an internationally known virtuoso and one of the best guitar players on the planet, so I doubt if he's got time to come and educate us, although a boy can dream.
I think there was more going on there than just that, too, Phill, for a couple of reasons. An instrument like that is going to have sympathetic harmonies ringing out all over the place. If you note, he never stops fretting on the guitar necks, even when he's strumming or picking on one of harps. A harp is also not going to be tuned like a guitar. Harps (and this is a harp guitar) don't get fretted at all. They're plucked or strummed, just like Matheny does in the video. It is by necessity tuned to something open, or even a full chromatic scale if there are enough strings for it.
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