I can't find anything on their website for you car, but he probably said that because he found a factory brake controller plug on your jeep. It's always best to use the factory plug, it'll have the most reliable connection and a clean looking install.
There are plenty of other brands that sell a direct plug in brake controller for your car. Here's an easy link.
https://www.etrailer.com/bc-2012_Jeep_Liberty.htm
I'd recommend a proportional controller, they are double the price but they are nicer if you plan on using it alot or just want to be more comfortable during your journey.