This graph seems to indicate that the Chinese anti-satellite test moved the number of objects from ~10700 to ~13900, or about 3200 objects released. Now that we are at about 16000 objects, 3200 is closer to 20% (in fact is is exactly 20%) than 10% of all objects.

Different sources will quote different numbers of objects.

The reason is that there were millions of debris particles. So you find counts of different sizes.

I got 10% by comparing the number in the Wikipedia article over a certain size with the number of objects that NASA is actively tracking. If NASA is actively tracking at a different size threshold, that would explain the discrepancy.

Regardless of the exact numbers, this Chinese test is clearly a significant part of the problem by itself. And the altitude chosen means that it will continue to be a problem for a very, very long time.