So the two-tile city = 2 pts. is no more? I didn't know that...
It's to do with the 1st edition vs 3rd edition rulesets. As RGG have now adopted the 3rd edition (HiG) ruleset, to answer the question from an official position, the 3rd edition does not have the small-city rule. Therefore, small cities are made up of two tiles at 2 points per segment (4 points total). The confusion comes as there are still sets of Carcassonne being sold that contain the 1st edition ruleset (which include the small-city rule). To be consistent with the official position, both RGG and HiG are using 3rd edition rulesets. This is what the CAR is based upon.
In the OP case, a one tiled city, using the official rules, is scored at 2 points.