You’re saying that it doesn’t matter because the US government is able to prove his citizenship, but that isn’t in question. The crux of this matter would be whether OP was ignorant of his citizenship and if that ignorance would have any relevance to his case.
Securing official documents only available to American citizens makes it more difficult to argue that he was ignorant of his status as an American citizen. He likely could still make a compelling argument (provided he acts quickly), but it does make it a bit more difficult.
Yeah, reading the article, it sounds like they’ve decided to park at the space station because the parts that malfunctioned during the journey to the space station were not designed to survive re-entry, meaning that they won’t have the opportunity to understand what went wrong with them after they return to Earth. So they’re delaying the departure in order to collect as much information as possible about what went wrong in the first part of the mission. They’re still confident that a safe return is going to happen.