Doe this relevant to the crime and relevant to social class? This is based on "Don't know much about crime" story.

I can't find anything about hatchback car.

And other thing, Englihman says Billy "sticks out like a sore thumb" what does it mean and does it relelvant to the crime and social class?

To stick out like a sore thumb is a metaphor for being REALLY obvious. If you are a criminal, you really don't want to be obvious at all.