Right, but that is because there is a lag in the data. Quarantines have only started recently.
And that says nothing for why the data matches up exactly to an ideal model and furthermore that model (quadratic) isn't correct for the spread of viruses (which is exponential).
If you look at data from outside of China, you can see a regular jagged line full of noise which you would expect for real data. The data from China stands out like a mannequin in a lineup.