People who can draw obviously can visualize space and objects in their mind. Therefore, people who can't draw obviously cannot. So does that mean that people who can't draw must have low spatial IQ?
Spatial IQ refers to the ability to perform navigation tasks, mental representation, and mental rotation of objects. Therefore, if you have a clear idea or 3D model in mind of what you want to draw but you are not able to reproduce it on paper, I would say does not mean you have a low spatial IQ.
No. Bad drawing does not mean low spatial IQ
However, the inability of drawing can depend on other factors. Check Neglect syndrome and clock-drawing test.