A little further down..

 

"An instant of regret that it was Galina or Erian he had stilled - he was not sure he had intended to do that; Lew Therin had gone on at length about how he intended to sever every one of them who had imprisoned him"

 

Hard to tell what really happened.  I think the bottom line is that what he used was a weapon to still those women, even if Rand, like he has done so many other times, figured it out as he went along.

I disagree.  He had ALREAGY broken the shield and was free - the Power filled him. 

 

Siuddenly it tore apart before him like rotted cloth.  The Power filled him, and as it did, he seized at those three soft points, crushing them in fists of Spirit

 

 

The "he seized at those three soft points, crushing them in fists of Spirit" was either revenge or an attempt to ensure that they did not once again link with others to shield him again.    What better way to ensure that than to Still them.