Question

In the scene where he is in prision and he needs to show the cell mate that is helping him that he is not lying about the whole thing. He goes back to the time he drew the picture, I don't know why he drew that picture can anyone explain? And when he went back to this time he smashed his hands onto those two metal spikes on the teachers desk. Wouldn't his cell mate in prision know Evan as having the scars on his hand as if it happened earlier on in his life?