This guy, Matteo Mancuso introduced a new left hand technique; he has been noticed by those guitar players which have notoriety, such as Steve Vai.
In this song, played the Van Halen way, he demonstrates how he uses his left hand fingers to achieve his peculiar style. The tapping is not part of it.
The technique could be assimilated to what Bass guitar players do (those that don't use a pick). He plucks the strings from above. Not to be mistaken with the hybrid picking country players favor, using a pick to pluck the bass strings and three remaining fingers to pluck, but not from above, from underneath the strings.