The ballot measure claims that the Quarry is zoned for "2.1 million square feet of commercial". That does not mean that such an intense volume of development is guaranteed or assured-- far from it.
The law is clear on the subject and is best summed up in the publication League of California Cities' Handbook for Commissioners:
"Zoning does not confer the right to develop. Some people misinterpret zoning regulations to mean that the level of development will be allowed automatically. Zoning confers no such right- it is merely a designation used for planning by local agencies. As such, it is always subject to any change the governing body sees fit."
While the current Quarry owner may claim a right to develop some huge amount of commercial with or without housing, no such right exists. He does have the right to propose anything his heart desires.
He may choose to submit plans for the maximum allowable square footage of development the zoning of the property permits. However, as it stands today, he is not guaranteed any amount of density whatsoever.
The November ballot measure would entitle the property to up to 355 units of housing. Voting NO means that, when an actual project is proposed, it must get a public vote for housing. But, if the ballot measure passes, Pacificans will never again get to vote for or against the housing because the land would be entitled.