My dd6 is artistically gifted, your son may be too!
We ended up getting her into a very casual art class which focuses on allowing students to draw/paint with a tutor making suggestions as to techniques to try every now and then. Sometimes they even step in a do a bit of the drawing themselves so the student "creates" an artwork they are proud of. Trust me the parents can tell when this has happened!
We did this because the rage to master got obsessive at age 5. and she was losing self confidence. It has been the very best thing we could have done. We also supply her with good quality materials, allow her to draw whatever she likes (good or iffy) she colours in pictures for relaxation although I've heard this is frowned upon. She does a lot of lead pencil drawings and cartoons for fun.
As for it being an indicator of IQ it's hard to say. She is HG+ and reads at a 10th grade plus level, I think though that the art is a talent that perhaps may have been there without the IQ. It's really hard to know. It just consumes her in a way that other things she is very good at don't. We have actually made the decision to stop pushing the school to cater to her giftedness (a futile task anyway) and just let her focus on her art. There are so many wonderful career options for artistic people these days that we would be incredibly supportive of her pursuing this.
As for your sons picture, it does look very good and intricate. My DD sometimes does similar drawings, perspective is starting to come out at this stage and there is a very wide variety in what is normal. Like others have said, more than anything it is a sign of being able to focus and detail which is definitely something gifted kids often possess. I think the thing that stands out when looking for creative giftedness is the rage to master, that obsessive quality to draw to the exclusion of other activities etc.
Good luck!
