^Yes, Gerrold did write the bulk of the original series bible. Although presumably all the ideas were developed in collaboration with Roddenberry, Fontana, and Justman. It should be all four of them who get creator credit for TNG.
Not my intent to slight the others involved.
It's just that was the first thought that struck way back when I first read that document. In fact it is Justman, IIRC, that deserves credit for the presence of Worf in TNG, for example. I'm sure there are other aspects of the series that can be traced back to any one of those folks individually and/or in combination.