Everyone knows whether or not he is a citizen. There’s no such thing as “reasonably believes”. That’s like saying “I reasonably believe I’m the savior of the world.”
Agreed, and the condition as written means that the alien must demostrate some reasonable basis for the belief that the alien is a citizen. A mere declaration is not such a basis.
Even Jesus Christ did not rely on His assertion, but demostrated under Mosaic, contemporaneous Roman, and even physical laws that He is the Messiah.
Ergo, we have demonstrable reason to believe Him to be One and The Same, even after so many centuries.
Interestingly, there is far more evidence to suport Christ’s existence and claims than, say, the existence of Plato, or many other ancient writers whose historicity we accept, in many cases based on no eyewitness accounts, but rather based on heresay evidence found in writings many hundreds of years later.