It is standard practice for the artist to retain copyright of any work created by them under copyright law. Although you have purchased the actual art you have not purchased the intellectual rights, these remain with the artist.
This simply means that the artwork cannot be reproduced without prior permission from the artist, however the artist can reproduce the image and any preparatory works should they wish. For me this would most likely be to promote my work and produce sales merchandise.
If you wish to re-create or produce any products using the artwork please contact me to discuss this in advance. A fee may be levied.