ALexban,
Well my FCTM says slightly different!
"<skip>
Look for traffic using the traffic display as an aid
Call out any conflicting traffic
Do not maneuver unless visual contact confirms that separation is not adequate.
Maneuvers based solely on a TA may result in reduced separation and are not recommended"
Sure nothing should be done on a TA when not visual, wait for the RA and follow it. But if he was visual it is a completely different story.
I'm not saying the Captain was right to do what he did, in fact I'm not commenting at all on his actions. But the QRH, FCTM and Ops manual give him the latitude to act.
Since none of us knows what really happened we'd best leave it at that eh?