I am assuming, that the creator of the puzzle is very very aware of what is going on here and is between us. I also assume, that puzzle 66 was not solved by anyone, but rather the creator himself did reveal it's private key after it's probably was taken by bots, to see test if bots are actually a threat for solved low-bits puzzles.

So i will not be surprised if we see puzzle 67 also out of no where gets it's private key revealed after sometime by the creator, sooner or later.

Mark my words.