The ending of the movie "source code"?

i didnt get it ! the ending i mean... coz i understood something completely different from what my friend did. i told her that he was able to change the past and prevent the explosion in the train and life just went on ..and she says that this is another life and its not real even the scene of the man informing the general that the explosion was succesfully prevented and the message that reached ingrid , that this was all not real and took place in the other life ?? which one of us is right ? or did neither of us get it right?