True, Twitter did apply the tactical rel-nofollow. Technically, Google is correct in their statement.

I don't care for how Google is positioning the statement, which sounds like Twitter is trying to hide its information from the public-at-large, and that Google is simply trying to deliver the best experience for the user. It's highly suspect for Google as the source of making those statements, as they benefit directly as a result of Twitter being included in their search results.