Most Fender tube amps, including the Deville, barely produce any volume at "2" and start to "grind" at about 4-5. I would imagine this player has a good clean boost between the guitar and amp pushing the pre amp, but not too hard. The result is a good full clean sound with some fullness to it.
This player is only using the clean channel of the amp, obviously cares about the levels, and has set the tone controls on the Deville where it will sound very much like a Princeton Reverb and at the same output levels. Good on him, and an example of what I preach constantly.
Exceptions may be the Princeton clones I build that can be turned up to "8" in most cases without distortion (trade secrets here). Maybe Steve Hurt will chime in about the Princeton clone I built for him.