That doesn't provide causation; you don't wake up on Tuesday, see a price change from Google on Monday, and change the keynote you are giving on Wednesday to rush through a price drop. If anything, it makes more sense to think that Google got word of the things Amazon was announcing at their conference a few weeks ago, and after some careful thought decided to jump Amazon's announcement so that they wouldn't look expensive.
His comment doesn't imply that causation happened in either direction.
I am not certain how to read the comment other than "it isn't possible for it to be reactionary as it happened first", which I believe I corrected (but maybe, as I demonstrated a stronger conjecture in addition, that doesn't count?).