Power is measured in Tflops. Performance is different. If a car has 300hp, and the next model is due to be released and the car company says it has twice the power, do you think he means 600hp?
Phil absolutely said twice the POWER. He didnt say twice the performance.
Performance of a console is different, and would take into account any efficiencies.
In a car, performance is how quick it is for instance, how fast it does the quarter mile, top end speed etc. Two cars can both have 600hp, but will perform differently. One could be quicker than the other. Theres more to speed than power. You have torque, how heavy is the car, what is the gearing like etc etc.
Same with a console. It can only produce 12tflops, but depending on what else has been done, that 12tflops can do more than double what 6tflops could do.
People who try and say Phil didn't mean the XSX has double the tflops of the One X, are like the people who say Cerny didn't really mean that the PS5 will have hardware accelerated Ray Tracing.