The referendum was removed from last week's ballot after a legal challenge by the state's Gaming Control Board.
Maureen Garrity, a spokeswoman for Foxwoods, one of the casino operators approved for a site, said the poll was "statistically insignificant."
"We've always said that only a vocal minority opposes casinos, and this vote is proof," Garrity said.
Dan Fee, a spokesman for the SugarHouse casino, the other proposed casino operator, said anti-casino activists had ballot boxes in "just 3 percent of the polling locations."
He said the votes cast represented less than 1 percent of Philadelphians. "This isn't a mandate, this is an embarrassment," Fee said.
City Councilman Frank DiCicco, who represents the district where both casinos are planned, has sponsored a bill to create a 1,500-foot buffer zone around casinos.
Although the idea got strong backing in the unofficial ballot, he said the casino issue is more a matter now for state lawmakers.
"The issue needs to be placed on the agenda of state lawmakers - the folks who gave us gaming to begin with," DiCicco said.
DiCicco opposes the sites for the Foxwoods casino in South Philadelphia and the SugarHouse project in Fishtown.
He said that, three weeks ago, he drove around with a representative of Foxwoods to look at alternative sites, beyond the boundaries of his district. He would not say where, adding, "I can't start a firestorm by mentioning where."
Casino-Free Philadelphia had red cardboard ballot boxes for voters in 57 precincts last Tuesday. Hunter said that at some polling stations, the question was inadvertently left on the ballot.
Of those accidental votes which were not included in the final tally - 835 voters supported the idea of a buffer zone, 359 did not.
Michael Seidenberg, a real estate developer and a Republican candidate for City Council in the First District, said people who voted in the unofficial referendum wanted to "defend their right to have a say in the matter."
"These are not anti-casino people; they're not anti-development people. It's about the process and location," he said.
Contact staff writer Jennifer Lin at 215-854-5659 or jlin@phillynews.com.