Ackman had bet that he would make $1 billion in his short against the nutrition-selling company, accusing it of being a pyramid scheme.
"It was a binary bet and it's dangerous. He was betting that the government was going to intervene and shut Herbalife down," Wapner told "Mad Money" host Jim Cramer. "There was no in-between."
Wapner's new book, "When the Wolves Bite: Two Billionaires, One Company, and an Epic Wall Street Battle," chronicles Ackman's five-year-long battle against another iconic activist investor, Carl Icahn.
In his book, Wapner, who now hosts CNBC's "Fast Money Halftime Report," recalls his experience as the host who refereed the billionaire battle.
"You could hear ... in the background, the 'ooooh' — those were the traders on the floor of the New York Stock Exchange," Wapner told Cramer. That day, "trading volume dropped 20 percent."
In the interview with Wapner, Cramer also honed in on one of the biggest mysteries about the Herbalife debacle to date: did Icahn bet with Herbalife or did he bet against Ackman?
"Maybe a little bit of both," said Wapner, who said "the access" to both Icahn and Ackman was what really "made the book."
"I can tell you that I don't think that Icahn would've made the investment against Ackman all by itself," the CNBC host continued. "You know, revenge is a powerful thing, but Icahn's not stupid. If he didn't believe that he could make a lot of money in Herbalife, he wouldn't have done it. Ackman was the cherry on the sundae, but the sundae already was looking pretty tasty."