How can you not notice that you are in the wrong car? Different people have different stuff lying around in their cars. Stickers, scratches, dents, dirt. Cars smell differently.
Long ago I was tasked with swapping someone's Porsche off to them at their house, as the service writer the evening before had given the customer the wrong car.
Both black. One a panamera (so?) 4, one a 4s. One with dealer plates (the one they ended up taking home..) , one with a custom plate.
So, after showing up to this persons house (through a golf course, up a winding top of the hill driveway), I knocked on his door and asked him the same question (after apologizing for the workers mistake).
"Oh, well, it was evening and the radio stations were programmed in the same, so I just didn't even think about it. In the morning I said "well, that's strange, usually they wash the car nicely before returning it -- then I realized it wasn't my car".
Guy was super down to earth about it, not a care at all and the exchange was very pleasant.
Point being: some people just really go with the flow, and even with 100k+ cars 20 years ago, sometimes just don't really pay attention to, well, much of anything. Bigger fish to fry, I guess.
I'll never forget the whole interaction, fully expecting a grumpy person and coming face to face with "eh, life!".
I definitely don't have a lot of stuff lying around in my cabin. At the moment the only things visible in the cabinet are an electronic parking disc and a 12V two-port USB charger. If I encountered a clean car with the same interior colours as mine, I might not immediately notice it.
And the same seat and correct mirror positions? Sure, it is not impossible, but I have a hard time imagining that one would not notice driving away in the wrong car.
