There is nothing in the above quote which explicitly states "Watchtower writings are now part of the Bible." I would argue that it is not even implied - I think they are referring exclusively to what is in "the Bible" itself.
And any JW apologist would (rightly) call you on it.
I think this is another example of Watchtower spin in action, as they go ahead and prepare the way for later on including all the boring GB directives into the final Bible of the beginning of the 1000 years. Remember, they have grandiose expectations. They like to write the future in advance, or at least throw out the options. They are not saying the current WTs are part of the Bible (at least not yet...).
They will, of course.
Randy