This is well known as Heisenberg Uncertainty Principle aka Uncertainty Principle or Heisenberg Effect, or in layman's terms, object under observation changes its behaviour or state and is therefore unmeasurable, or as stated by Werner Heisenberg, "The more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa."
They key exchange is a slight variation of or not that much different from PGP (Pretty Good Privacy) public-private/symmetric keys mechanism, developed and published by Phil Zimmermann in the early 1990s, except in this case it's fortified by the use of quantum mechanics to make even the key exchange impossible to tap without breaking communication.
Nothing here is revolutionary, the idea of the practical and inexpensive secure quantum net communications using fiber optics (or even "fixed wireless" lasers) has been around for more than 15 years. The scalability has been tested and established when Abilene Project gave way to Internet2 in 2007.
So while I find the theory interesting, I also observe that theory does not over come the physical reality. This is why I chose the wording I prefer physics over meta physics.
It is easy to over think a problem. An interesting example, in the space race, it was found that in zero gravity a ball point pen ceases to work. America spent a million dollars developing a pressurized ball point pen to work in zero gravity. When one diplomat bragged about it to the Russians, the Russian just laughed and said “we just use pencils”.
I took that incident as a life lesson. But to give it a try at least, if I think of a quantum physic theory, and am able to prove it, it then becomes simply physics. Therefore the measurement of any quantum physic idea changes it so that it no longer is Quantum physics... How did I do? -grin-