You're clearly correct about vent sexing, but the story about the planes rings more true. It reminded me of a study that shows that car enthusiasts and bird watchers access the area of the brain normally used for facial recognition when identifying cars and birds, respectively[1]. I would expect that plane enthusiasts learn to identify planes much in the same way that car or bird enthusiasts do.
I think another factor is almost certainly sound. The study I just cited dealt with photographs, but the plane watchers in the story would also have been able to hear the sounds of the planes. There are certain models of aircraft I can identify by the sounds of their engines alone because I have been around (or in) them so much. However, to most people they just sound like "jet noise" or "prop noise." Even though I can tell the difference, I would have a hard time explaining it because the vocabulary we have for describing sounds is not nearly as complete as the vocabulary we have for describing images (or at least my vocabulary is that way).
I think another factor is almost certainly sound. The study I just cited dealt with photographs, but the plane watchers in the story would also have been able to hear the sounds of the planes. There are certain models of aircraft I can identify by the sounds of their engines alone because I have been around (or in) them so much. However, to most people they just sound like "jet noise" or "prop noise." Even though I can tell the difference, I would have a hard time explaining it because the vocabulary we have for describing sounds is not nearly as complete as the vocabulary we have for describing images (or at least my vocabulary is that way).
1: http://cognitrn.psych.indiana.edu/rgoldsto/courses/concepts/...