The amazing thing is that I had earlier seen the acquaitance at the same event, and I hadn’t noticed a difference in hair colour (different hue, same degree of darkness) between the two, possibly because I focus on faces and voices more than hair.
How did this error happen? Well, the stranger was a sibling of the acquaintance, of the same gender, build, age and hairstyle as the acquaintance, and both were attending the same event, and both have quite distinctive faces with a strong family resemblance in the entire face, not just in a couple of features. The family resemblance brings the siblings’ faces closer in similarity of appearance, while the shared distinctiveness of their faces pushes them away from resembling the faces of any randomly-chosen face of an unrelated person of the same race, age and gender. I would even argue that my misidentification was in fact a correct identification of pretty much the same face that happens to be shared by two people rather than the one individual, as is normally the case with faces, rather like the situation in which you meet by chance the twin of a person you know when you weren’t aware that the person you know has a twin. No, the siblings both now known to me are not twins. Yes, other people have made the same mistake in identification.
Is there anything to be learned from this mistake? I guess it shows that at least in my case, super-recognition is not about having a photographic memory or a memory for every single visual detail, but is more to do with detecting similarity, not just in one or a few visible features, but in an entire pattern made up of features, which as a whole can be distinctive, memorable and identifiable. Is super-recognition a superiority in memory for visual patterns?