Ridley says Deckard is a replicant. Ford and I believe the script writer say he was always a human. The idea didn't become widespread until after Ridley released his Director's cut and he finally revealed/claimed it to be the case.

It started out as a cool idea, but I've been seeing it rejected more and more lately by hardcore fans, with people pointing out the fact Ridley didn't insert the idea until he was preparing a huge release of his cult classic on DVD/Blu Ray. This was back when extras and boxsets and Director's cuts could really drive sales and so the change was made in retrospect basically to sell DVDs. I sort of thought that seemed an overly cynical way of looking at it but I'm starting to come around to the idea myself.

For one, you have the writer and Ford himself finally coming clean and admitting he was always a human as far as they were concerned. Two, as cool as the idea is, it sort of ruins a lot of what made the theatrical version appealing. The subplot of the romance between a human and a replicant. Deckard falling for Rachael, someone he's normally charged with tracking down and killing. That also ties into Batty's ability to value a humans (Deckards) life at the end, which has a lot more meaning and weight when it's juxtaposed to the way Deckard views replicants. All of that is altered or removed by the idea of him being a replicant. It fucks up a lot of the philosophical themes of the original version.

Anyway it's early and that's a little more of an explanation than I expected to give when I started replying. So I'll close out by saying it's taken me a while but I think the movie works a lot better with Deckard as human, and it's still under debate by it's creators as far as I can tell. We'll just have to wait and see if 2049 has any more answers.