The person you replied to does not say that China's political system is better in any way, simply that if such a system (single party authoritarian government) can out develop the US then there must be some serious improvements to be had for the US's democratic system.

In other words, if China can give their people what they want without fair elections or due process or freedom from corruption then our democratic system which ostensibly includes those things must be seriously broken. That does not mean authoritarianism is better. At least that's how I read the comment.