They are using a double negative here ('Un' and 'not'), so it means that they are saying that the foreign policy was American.

His foreign policy can be accused of being short- sighted and naïve. Un- American it was not. "short-sighted" means you're thinking or planning only for the immediate present, or the very near future (like tomorrow or next week, or next month), and you're not looking at the long-term consequences of your actions. (You're not looking "far" into the future). "naive" is hard to describe. It means . . . your level of understanding is not mature. "He never lived in a city before. So when he moved to New York, he walked on the streets alone late at night. He was naive as to the dangers of the city". Un-american = to have values that are contrary to values held by Americans. To me, when I read this sentence, I think that there was some group of people who were criticizing someone, maybe a president for his foreign policy, by calling it un-american. The author doesn't agree that the foreign policy was un-american, but does agree that the foreign policy deserves criticism, and that criticism is that the foreign policy was "short-sighted" and naive.