The point the article was making is that transactions can and will be deemed illegitimate, both in the sense that mistakes are made, and in the sense that the legal framework will decide you have to reverse the payment. If you've buried cash and refuse to tell people where it is, you are in roughly the same place as refusing to reveal keys. You can be held accountable of course, in various ways.
I think the article was more making the point that any payment system that doesn't recognize this reality will have inherently limited uptake, which is probably true.