I never said it was an accidental
I don't know the details of the device used, but in general in space there is no need to explode anything. Just kinetic energy from hitting it that fast is enough for total destruction. For instance the recent US effort to destroy their aging spy satellite did not use an explosive, they just ran a rocket into the satellite.
At the worst you might explode the missile very, very gently before impact to guarantee multiple impacts. I have no idea whether China did that, or just collided them. I assume collided.