Is the man in the flashbacks really the Man in Black?

In Season 6 E15 it is shown that Jacob and the Man in Black are really twin brothers and are raised by the mysterious woman that lives on the Island who grants Jacob the powers of the protector.

However, when Jacob discovers his brother murders their 'mother', he is filled with rage and tosses his brother into the Source of the Island.

What happens here is the question at hand, the Smoke Monster comes out of the Source and begins to take the shape of his brother, implying that they are one in the same, however, his brother's body is still present, and is buried with their 'mother'.

So did this man become the Smoke Monster, or did Jacob simply awaken the smoke monster, with his rage?