Occam's razor. We know that someone recently stole the exact information they are complaining about being exposed. This is probably how the agents were compromised.
A lying anonymous government source (from one of the governments that has anonymously lied to us so many times in the past) is far more plausible than some bizarre 2 year delay and subsequent cryptographic breakthrough by the "Chinese and Russians" (who are now allied?).
He could have done a worse job encrypting them than he thought he did.
He could have purposely handed it over:
for revenge because the US is trying to hunt him down;
because Russia threatened to hand him back to the US;
because Russia tortured him for the keys;
etc.