I have a theory that some people have very low visual accuity.
It's as if they don't see detail in objects, only the rough shape and color. I personally know lots of people that can't tell cars apart even when they're completely different models.
Of course then you have other people who are just automotively ignorant. They're the ones that couldn't tell you a single fact about their own car outside of it's color and make. Those kind of people couldn't tell you if they had a 4cyl, V8 ofa nuclear reactor under the hood. They just don't care.