He is serious about a Presidential run. Not just playing around. He now is a credible candidate instead of a politician wanting to gain attention. He's real.
As to the announcement, that he is not going to run CD3 is the gist; see this link.
He might be better than Biden, and is younger. Now that he's proven serious, it is worth taking him seriously. It is early in things, so keeping an open mind has no downside.