User blog comment:EvilLamp/AVGN / Board James Confusion/@comment-1705775-20151121212629

it is technically a theory but HEAVILY suggested in-universe since Board James descends into madness and during the Full House episode it is revealed he suffers extreme delusions and his "friends" may not of been real.

The episode in which Nerd seems to act as a malicious alter-ego is when Board James plays a bunch of board games based on popular video games, Nerd appears as a kind of floating head and mocks the board games in his usual style.. it gets darker near the end however as Board James starts to take on more of the Nerd's personality and at the end of the episode Board James appears to completely change into the Nerd.. it is thus suggested that Nerd is one of James' personalities that he suppressed but eventually took over as the "dominant" one.

Yes, it is comedy and not meant to make sense and you can argue it may not be "canon" but the episodes exist and from what I recall Nerd was definitely suggested at being Board James after Board James went nuts.