This is a potentially stunning and revolutionary find.
However, I must say that I would be extremely surprised — which is putting it mildly — to somehow find that the document actually predates Muhammad. If that were true, of course, it would undercut the entire standard story of the rise of Islam, not only as faithful Muslims have believed it but as scholars have reconstructed it.
However, carbon-dating simply isn’t that precise, and the allowable range indicated here — AD 568-645 — does permit the text to have been written during or immediately after Muhammad’s life (AD 570-632), which I think far and away the most likely scenario. I can’t think of any reason, off hand, why we should lean toward the earlier of those two dates rather than to the later.
That said, having so apparently early a text is, in and of itself, astonishing.