Perhaps more interesting is the question, why did Ridley Scott give away the answer?

After all, the point of these things is the ambiguity - that these stories, like poetry, say more in saying less. We learn more, experience more, by wondering ourselves if he is human. The defining elements of humanity were of concern to Philip K. Dick: what makes us human? Why do we have no good, definitive answers to that question? Why do we often not meet our own standards for humanity? - and he spent much of his writing career preoccupied with those and similar issues. The formats for these explorations were very imaginitive, but the important unifying element was the matter of doubt - which can move a story along with the paranoia and xenophobia that is inherent in our culture, but also forces us to tackle the question in a meaningful way, to really confront the issues.

If it were meant to be so black and white, he would just have written an essay.

So, why spoil the fun? And why now, after decades have passed? There are a few theories:

  • Scott wanted to settle a longstanding grudge with Ford over the issue. (During the making of the movie, Ford pushed hard for Deckard to be more human, or at least to obscure the evidence - this was arguably good drama, but at the time it could have been seen as egotistical on his part.)
  • He was having a bad day/hung over/was annoyed with the reporter, and did it on a whim.
  • He did it to intentionally mock the people who've been obsessing over and debating the question all these years - whose often terminal pedantry would have remained comfortably hidden from him, but for the wonders of the internet.