What do you mean by drawing sand? What does Jay Chou mean by painting sand?

Painting sand originally meant that ancient calligraphers painted some landscapes such as deserts. Later, it was used to describe the artist's brilliant painting skills and rich connotations.

As for "draw a picture with quicksand in your hand", I personally think it refers to sand painting, in short, painting with sand. There are programs inviting sand painting artists every day. The picture below is a sand painting.