You must be thinking of something else. Matthew Green has said he would have much rather got this implemented in BitCoin.
ZCash forked off of BitCoin because BitCoin core wouldn't accept it. The proposed solution was a "side chain" to BitCoin. Side chains have been being talked about since around 2009, and that's all that is happened: talking. There is no code and no agreement on how they should work.
The fork happened when it became apparent that this would never make it into Bitcoin in any form.