>> "Re-built" means "recompiled", not "rewritten".

> Don't the code have to be rewritten if you update it?

The source code of the very few updated components would have been updated, not necessarily rewritten (of course we can argue which percentage of the source code of a component would have to be altered in order to be classified as a rewrite of said component). Everything else has likely been left untouched from olsen's port.