Watch the Open G Exercise 4 online guitar lesson by Richard Gilewitz from Fingerscapes
Simply put the 1st note of the piece could realistically be treated as a 16th note but there seems to be a great effect by 'popping' that 1st note in a sense by striking it more forcefully with the right hand 'a' finger while releasing the pressure immediately on the left hand finger following the strike. The trick is to keep the finger touching the string upon the release thus avoiding extraneous sounds. This also makes a strong announcement of a piece of music which demonstrates confidence from the player. Pay carefull attention in measure 8 when the 'm' finger is actually utilized 3 times in a row. This seems to be somewhat unavoidable and I don't like using the same finger twice in a row let alone 3 times. However, you are only dealing with 1/8th notes and you can actually create a nice 'vamp' sound. Play the final chord as a broken chord wherein you create a slight roll with the right hand separating the picking fingers in time.