In his his December note explaining why he covered his short, Tilson said he received information that indicated Lumber Liquidators' management may not have known it was selling the laminate.
"In the past week, I've received information that leads me to believe that senior management of Lumber Liquidators wasn't aware that the company was selling Chinese-made laminate that had high levels of formaldehyde," he wrote. "If this information is correct, then the company was sloppy and naïve, but not evil."
One of the factors leading to his renewed short position, Tilson said in his Tuesday presentation, was an announcement from the Centers for Disease Control and Prevention that it had revised an earlier report on the laminate flooring's safety, concluding that people exposed to some types of products were three times more likely to get cancer than previously estimated.
The CDC said it had used an incorrect value to calculate ceiling height, which meant its estimates of the airborne concentration of cancer-causing formaldehyde were about three times lower than they should have been.
"When you associate a business with the word formaldehyde, that's bad. When you associate it with the word cancer, that's devastating," Tilson told CNBC.
Citing his "most reliable source," Tilson claimed Lumber Liquidators' business "has just gone off a cliff" in recent weeks.
—Reuters contributed to this report.