I wouldn’t be concerned about it. Not very often does a Leonardo da Vinci— who was great in art, architecture, science, engineering and poetry—come along. Most of us are good at some things and not so good at others. If your son truly “knows how to read” (even if you mean he can identify a few common words), is a good athlete and is on target in all other aspects of development, I wouldn’t worry that he can’t draw recognizable objects.
If you want to encourage progress in this area, I would suggest that you make certain he has plenty of toys that help develop fine motor skills and eye-hand coordination. Good examples would be puzzles, small building blocks and sorting games. Make certain which hand he prefers; many children his age have not fully declared their handedness. Help him use the preferred hand as much as possible. But don’t even give him paper, crayons or pencils until he asks for them.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.