The tone here always struck me as being skeptical of there being any true ruler to be found. Traditional readings, however, take it to be announcing that there is one. The grammar allows us to read it as a question or as an assertion, but the context make the assertion a little queer. Zhuangzi's next response is a classic skeptical response. The absence of evidence doesn't show there is or is not a metaphysical self.
Existence is one thing and evidence for it another.
It is hard to see what grounds we have for reading this sound skeptical observation as asserting that what we have no evidence for exists. The interpretive issue here is complicated and a number of responses are possible to preserve the traditional reading. Ultimately, I think the conclusion depends on how one can make the account coherent with the criticism of Mencius. Zhuangzi's analysis continues the view we noticed earlier. The heart changes as it goes through life-just as the rest of the body does.