It seems what it says is that PSA is < 0.1. The general view is that it can be scientifically determined that 99% of the cancer cells are dead or removed. There is currently no technology to determine whether the remainder 1% exists or not. The clinical experience is that the amount of abnormal cells is so small, and/or so inactive that it does not do any harm. Probably for years. Hope that helps.
Dont mind me. I am just another layman trying to make some sense of the whole thing.