Playing in a friendly actually cap-tied him because he is not a U.S. citizen. If he was a U.S. citizen and played in the friendly, it would not have cap-tied him.He's not cap tied to Ghana. he only played in a friendly which is meaningless.
FIFA have amended the rules of eligibility over time. You can read them in detail here but in a nutshell you can play for a country whose citizenship you hold, provided you meet some basic conditions: either you, one of your parents or one of your grandparents were born there or you lived there continuously for at least two years and you have not already played in official competition (including youth tournaments) for another nation.
That's the general rule, but there is an exception. You can play for another nation (provided you fulfill the other criteria) even if you've already appeared in official competition as long as it wasn't for the full national team and you already had dual citizenship when you made those appearances. That's how Diego Costa was able to play for Spain after turning out twice for Brazil in friendlies.
http://www.espnfc.us/fifa-world-cup...spirit-of-international-football-gab-marcotti