What kind of growl is this?

A sweet sweet chi mix I rescued a couple months ago. He was just leaning against me on the couch while I played a game on my phone and out of nowhere started quietly growling into space at seemingly nothing. He stopped when I spoke to him but then he started again so I got up to look for what he was growling at. Then when I sat in front of him looking at him he increasingly growled to this noise in the video. When I left the room he followed and started wagging his tail. He then whined at me, ran back into the living room, and got back on the couch and started licking my hand and asking for belly rubs.