[karpach]

It's not a felony because you are not faking a passport. There is no Conch Republic, hence having a document that looks like a passport with the emblem of the Conch Republic is merely a novelty item. Not a fake document. Now having a fake passport with the U.S. emblem would be illegal.

[PBRSTREETGANG]

Perhaps Atta used this novelty passport in places to test how hard they were actually checking the legitimate documents.

(If not questioned he knew just how lax they were. If discovered he could laugh it off as a mistake that the "Conch Republic" passport somehow wound up in his official documents.)