There are two things going on with this song that might not be immediately obvious. Firstly, Dave has his guitar in Drop D tuning (i.e. his lowest string is tuned down a tone to D). This allows him to have the droning bass all the way through the song. And secondly, as you have already identified, he is constantly pulling off the first note he plucks to the open note of the string he is playing on.
The song is also a decent workout for the picking hand (I'm pretty sure Dave uses his fingers rather than a pick to play this). Considering guitar is not his primary instrument, he sure plays a mean guitar.
It's a fun song to play on guitar, but I haven't tried it on Uke.