We’ve seen lots of aircraft and birds though, even if we haven’t spent much time actively thinking about them.

Even by the time we’re young children, we’ve been exposed continuously to something like tens or hundreds of terabytes worth of visual and aural information that informs our ability to recognize things. I think it’s very rare that people see something that they have no framework for recognizing.

I know personally that I could identify distinctive aircraft from a single viewing because I’ve paid attention to a lot of aircraft, but I struggle with bird identification because I haven’t ever spent much time looking at birds. Even given a picture of a bird, I’m not that confident because I don’t know what characteristics could be common to other similar birds and what are distinctive.

Birdwatchers are able to easily identify birds based on a couple pictures because they have seen thousands and thousands of birds.

This feels sort of related to the study that showed that chess grandmasters had much better than average memories for the positions of pieces, but if the positions were random and not from an actual game, their memories were no better than amateurs. We rely heavily on things we “know” even when that knowledge isn’t exactly conscious.

The aircraft/bird example is good. I too, can recognize aircraft easily, because I've seen a lot of them (both real and in photos/videos/drawings/3d models), and the distinctions mattered to me. Show me a bird photo, and a while later, give me a book containing this very photo + 50 others, and I most likely won't be able to find the one I've seen. Definitely not by any clues on the bird itself. It seems to me that you need some commonality with a whole category of objects before you even start paying attention to details of individual objects.