Lol, you read it again.
Two-thirds of cars made in Mexico are shipped to the United States.
And a good portion of that remaining third probably goes to Canada, from which auto plants have also been relocated to Mexico.
The part about exporting from Mexico to Europe just disoriented you. The main reason to locate in Mexico is to export to the US and Canada.
NAFTA was signed almost 30 years ago, and was formally effective on January 1st of 1994. I can assure you that the doubling of production in the last ten years associated with "fewer tariffs" has nothing to do with NAFTA.