I thought he was a liar too, but for a different reason. He claims he can take away bending forever, yet all we know for certain is that he can take it away for about a minute. He had the opportunity to rob korra of her powers, yet didn't, claiming it was "too soon". What if he actually didn't do it because she would realize he didn't have the powers he said he did, and reveal it to the public. It would be far more effective to let everyone THINK that he could do it