I am including a file from Inkscape that has double lines in CC. The same happens when I trace the image in CC and it doesn’t seem to matter what the settings are in the trace options.
I don’t think you’d want to resell it or use it in a commercial project, but if it were me, I’d feel comfortable using it to make something for myself or as a gift, but only once. IE no commercial use.
Here is their disclosure:
Note: All coloring pages are offered free of charge and for personal use only. The images are either royalty free or distributed widely on the Internet, and they are of unknown origin for the most part. All copyrights to images belong to their respective owners. For any problem related to copyright, please contact us or fill out the DMCA complaint Form, we will remove the coloring pages that should not be present on coloringlibcom as soon as possible. We also have a privacy policy to protect your personal data.