rajan, told you the same thing in the other thread you started asking the same question. It is a common mistake for people who don't know better to refer to every dog that has a bully look as a "pitbull". That doesn't make them one though. The only true pitbull is the American Pitbull Terrier, which is a small terrier.
Your friend that gave you the puppy misinformed you by telling you that the dog he gave you was a pitbull.
As I said in the other thread, it doesn't matter what the breed is. Just love him as your dog.