China's economy didn't grow at an 18% annual rate between the fourth quarter of 2020 and the first quarter of 2021. Rather, it was 18% larger in the first quarter of 2021 compared to the first quarter of 2020. This is how China always reports its numbers and always has. It reports it every quarter, but it reports it at an annual rate. News reports sometimes use the word "quarterly" but what they are referring to is a year-over-year figure.
The US reports differently. The 6.4% isn't saying the economy was 6.4% bigger in Q1 2021 compared to a year ago. It's saying it grew at a 6.4% annual rate for the quarter Q1 2021 compared to Q4 2020, or that it was 1.6% bigger in the Q1 this year compared to the previous quarter, since 1.6 x 4 = 6.4. This is how the US always reports it as well.
What was China's actual quarterly growth?
When compared with the last three months of 2020, the Chinese economy expanded just 0.6% in the first quarter of 2021, slowing from a newly revised 3.2% quarter-on-quarter GDP increase in the fourth quarter of 2020, according to data released Friday by the National Bureau of Statistics.”
The 0.6% quarter-on-quarter growth x4 is 0.6 x 4 or 2.4% at an annual rate. This 2.4% is what compares directly with the 6.4% US figure.
The 0.6% growth rate is coming after a very strong Q4 2020 growth rate (6.5% YOY, 2.6% QOQ), which is more than the 6% YOY growth rate of Q4 2019.
In any case, China's growth is back to normal now. Q1 2021 has a very high YOY growth rate because of the negative rate of Q1 2020. The entire 2021 will have a higher than normal YOY growth rate (8-10%) because of last year's low base. So China will not only be back to normal, but also recoup some of the loss of growth last year. That's more than you can say for most other economies in the world. That's all. The western media don't feel good about this and just try to spin the numbers to paint a different picture.