Help: car accident-cheating???

I just had an accident. Someone hit the back of my car. That guy got a ticket for following too
close. When it happened no emergency was called. Yesterday someone called me and left a message.
Today I called him. He said he works for emergency service and aksed me if I have any pain.
And he gave me an address for physical exam. I really don't feel comfortable for my neck and chest.
So I went there. That place is a rehabilation center. They gave me an exam and treatment, and
tell me to get more treatment. They copied my medical and auto insurance cards. And told me they
will take care of the charge. All these is weird. How did that guy know my home phone number and
how did they know I just had an auto accident? Is that a kind a cheating. I asked them for a receipt of today's treatment. It showed the total charge is $295 (~20 min). Do I need talk with my auto insurance about this treatment. I am afraid that I need pay this later.

I have no any experience on auto accident. This is weird to me. Any information will be greatly appreciated.