I think he does close to what I do hit the bass note with thumb and strum down then hit next bass note with thumb and strum down all the while the fingers play the melody. Sometimes I think he does a patterned bass. IE Thumb hit bass note then hit other note then hit the bass note then hit other note again like Chet Atkins does. Then he uses the index middle and ring fingers to play the melody all while doing that bass line. For a c chord a simple bass pattern would look like.
d-----2-----2-------2------2
a--3-------------3-----------
e---------3------------3--
but a lot times I think he strums down in place of hitting that other note (in the example the E note)
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