Here's the fact that is tripping you up. Having a y chromosomes is STRONGLY correlated with having a penis, masculine traits, and the feeling that your male. Yes, someone may not have been tested, but if you are in an elevator with 1 other person, and when you turn your back to them a sharp, stabbing pain starts in your shoulder, and when you turn back you see that person holding a bloody knife, you assume they stabbed you. Even if you didn't see it, and even though its possible a ninjas jumped through the maitenence hatch, stabbed you, and shoved the bloody knife into the strangers hand before leaping away, you can safely infer a much simpler chain of causality. To consider otherwise is academic at best. Those genes tend to manifest in noticeable ways. That's their job. The prospect of an individual who is completely and unambiguously male, with no traits or feeling inconsistent with maleness, who is Xx, is so remote its not really useful to consider. Unless you have evidence to the contrary.