What Grey said was that if the Town ignored the plebiscite and approved the rezoning, the No side would likely fail in any action against it. While that might be true (for a variety of reasons), the converse is not. Were the Centre to pursue a Charter challenge against the Town, the outcome would undoubtedly turn on the proponent's ability to show that the vote was patently biased. Other than the uncorroborated musings of the mayor (hearsay), neither you nor Grey has thus far cited any such evidence.   

Indeed something the mayor did say undermines his own reported suspicion of bias. He said that if the entire town had been eligible to vote, he is confident it would have passed. Most rational people would infer from that comment that the motives of the 19 were not disqualifying from a Charter perspective...that is, they had other, legitimate reasons for saying no. Certainly the onus would be on Grey - were he representing the Centre - to demonstrate otherwise.