It means that there are many people in the car.

A horse, a waterwheel and a dragon are still talking about traffic. It describes a continuous lively scene with many cars and horses coming and going.

The description of horses and chariots is very vivid.

Bustling describes people coming and going, very lively and crowded.

Bustling: the appearance of harmony; Bustling: a chaotic appearance. Describe people coming and going, very lively and crowded.

For reference!