This fender tag does appear to be for an export car because of the "I" at third line up, second position, where U=USA, C=Canada, and I=Export.

But there were plenty of American cars in Germany that weren't cars built for export, because the shipping of cars to and from Germany was a free moving perk for officers and some non-comms in the military. This Challenger could have been shipped to an American serviceman in Germany who moved it back to the US.

Probably most of such American cars in Germany were shipped free back to the US at the end of a duty tour, but some remained there because they were sold to another service member on the base. For example, the owner of this '56 Chevy pictured at the Belgium World's Fair grounds in 1966 was owned by an enlisted man stationed in Fulda, Germany, who did not get free car shipping and likely re-sold the car to another service man on the base when his tour of duty ended. The owner of the Chevy and I had just come from the 1966 Le Mans 24-hour race where Ford beat Ferrari and won 1-2-3.