I believe he is in open D tuning which is why the sound is so full despite only 4 strings. Open tunings are great for playing jangly lead but I find them hard to construct non solely instrumental songs around. Goo Goo Dolls used them a lot.
Discussion
As soon as you said it, its all i can hear. I like to Look at his guitar in video, dude is slowly destroying it. Thank you for the technical insights
The Bazaar by the Tea Party is another good example of open tuning. I believe it is a variation on open D as well but it has been some years so don’t quote me on it. But you can definitely catch the alternate tuning in that song.