Being a Brit, I've only just seen this episode and I have to say the Carrie connection instantly seems to me to be with the Others rather than Walt. The mind thing does suggest Walt but the whole being the "underdog" thing points to the Others.

They refer to themselves as the good guys, which suggests there has to be or have been "bad guys". Perhaps they were once the victims or subjects of whatever testing was going on, probably at the hands of the Dharma Initiative and they now have the power to rise up against that, becoming the power holders over the Losties and perhaps even being out for revenge against the real bad guys ...