... and there it goes, any credibility I would give the author. There's dumbing down the content for a non-technical audience, and there's not understanding.
1. Hashes don't "sign" things (not directly anyway)
2. Hashes aren't unique in theory or practice (using a 256-bit hash on every 257-bit number will generate 2^256 collisions by the pigeonhole principle).
Suppose every person generates 1 billion files a second * 7 billion people * 1,000 years = ~3x10 ^ 28 call it 10^29. For a collusion among non identical files using a good 256 bit hash you get ~1/(2^256) * (10^29) * (10^29) = ~1/(2^198).
Or 1 chance in ~4 * 10 ^ 59 of finding even one collision.
[0] http://preshing.com/20110504/hash-collision-probabilities/
[1] http://www.wolframalpha.com/input/?i=%281+billion+*+7+billio...