Satan??? What did I say that was so wrong?

Suppose this was the first time you were reading Mark’s words in his Gospel 8:27-38 Mark 8:27-38. You might wonder if these people really knew each other or if they had an identity crisis. On the one hand Jesus asks "Who do people say that I am?" On the other, his close “friends” who are all over the lot, respond "John the Baptist,” and others, “Elijah,” and still others, “one of the prophets." Now, this is after they have seen him feed thousands; cure the sick; raise the dead, and cast out demons. This is also after he’s provided enough clues as to who he really is.

Then, after Peter, comes up with the right answer, so we think, and proclaims “You are the Messiah.” Jesus turns to his disciples and rebukes Peter…and calls him, “Satan” and tells him that he is setting is mind on human things, not divine things.   

Now here’s a loaded question, which of the two is confused? I did say it was a loaded question but, in fairness to Peter why did he get it wrong or does even get partial credit?