The phrase that I would have used if I were a journalist would have been
Former Polish Native Won't Return To Socialism.
The way I read it, if you say Polish Native (or whatever country) it would apply that the person is a citizen of that particular country, but not a US citizen. Now the word former shows he or she is not a citizen anymore of that country but a naturalized citizen of the US
Maybe, but journalists prefer more succinct style. BTW, you cannot stop being a citizen of other country easily. Polish Constitution considers as Polish citizens even children of Polish citizens. So if one of your parents is/was Polish you could be drafted to the army when visting Poland (same thing with France, Greece, Israel and many others). Also to resign from American citizenship is not easy (some people try it to avoid the taxes).