I’ve found myself in the embarrassing situation of not having two stories to compare; however, a slight analogy with ‘An Occurrence At Owl Creek Bridge’ should be observed: dozens of clues are given to the end result, but they’re also misleading at the same time.
Although the readers may sense the irony throughout, they likely perceive it being only against the preconceptions of ‘civilised and tender white people’ and ‘barbaric and rough black people’ when it ‘turns out’ that Desiree is partly of black origin. The facts otherwise seem to be in order. Seeing an austere white man who is softened by love is just natural, just like a ‘black woman’ who seems to be simple in her emotions and was a foundling anyway.
Overrating of genetic differences’ relevance is affected in two aspects in the story. The more apparent one was discussed above, and the other one is overvaluing the state of being a descendant of great families; it's half cultural even for Armand, though, since he rather talks about ‘names’ than ‘blood’. In addition to the above preconceptions – which lead Armand to a ridiculously immature, yet also disastrous decision – another related problem emerges. When Armand turns out to be the ‘black’ one, one may comprehend that Desiree wasn’t that plausible to be the culprit, after all; we’ve just found that logical because we wanted to. If a situation is supposed to be logical, then it will usually seem to be, and that is what makes preconceptions really dangerous.