My oldest daughter reminds me of this.
She REFUSED to draw anything, until she was about 3 1/2. She went from drawing nothing to drawing people completely dressed with clothes. She focused on this until a few months after she turned 4. She began drawing 3+ hours a day on the whiteboard, and did that for about a year. We are talking about quite elaborate scenes/stories.

Even now, she generally goes straight to the whiteboard after school.

I think it is a sign of several things.
a) I think gifted kids do in general see the world differently. Because of that it makes sense they have more details in their drawings.
b) I think it also shows artistic ability.


Of course, my other daughter began drawing just as prolifically on the whiteboard right before she turned three, and her first tadpole person was right at 2.

Because of that my 'norms' can be a bit off sometimes.

Tammy