I took the time to read the Parole Board decision. I've also read everything I could find in terms of the reports on this situation. It seems very clear in this case that this man was not given proper rehabilitation services for the whole time he was incarcerated and that the evaluation of his risk to reoffend was not done in any serious way.
The decision was based mostly on his behaviour with other prisoners in prison. We know that men who are violent towards women and only towards women and only in intimate and sexual settings tend to be well-behaved around other men, and that's not in any way an indicator of their risk to reoffend.
It seems pretty clear that this man was a particularly high risk and that it was considered acceptable to put sex workers in the position of facing that risk, while other women were not considered to be good candidates for being around this man.