what do cops look for?

x whatever on the stolen car theory.

I've only had my VIN # checked once, and that was on my motorcycle. Sportbike's get stolen a lot, and I was leaving a motorcycle event so there were a ton of bikes (and hooligans) in the area, so that made sense. But I've never had my VIN checked against my paperwork in a car.

My guess is they had a report of a stolen Ferd that was close in appearance to your aunt's. Two officers in the car also suggests they might have been training, so you probably got the extra super-duper by the book stop.