I saw the conversation you speak of. I did not see it as out of the ordinary for a site geared to recovery from sexual abuse. That kind of conversation takes place routinely in the chat room. The other user took the responsibility for himself and took steps to take care of himself when triggered.
Yes, as Larry says, it's good to offer a warning, but one never knows who may be triggered by what, and in the end part of the healing process is learning to protect oneself in the event one is triggered.
Lots of love,
"Life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways, totally worn out, shouting 'Holy Shit! What a ride!'" ~Hunter S. Thompson