The 2009 bluray special features for the Narada said it was capable of transwarp drive. If the NuEnterprise got sensors scans of the Narada's propulsion system in action. Admiral Marcus/Star Fleet Intelligence/Section 31 could've figured it out. Also they did collect Scotty's transwarp beaming equation from him according to Scotty in the film. Maybe that's how they applied it to the Vengeance.