That's a good question. If the rendering was a PNG file, then there might still be a problem, depending on how far the copyright owner wishes to stake a claim. For example, if I take a photograph of a statue, the copyright owner of the statue could claim my photo breaches their copyright (this is not theoretical, it happens). A court may decide on various grounds whether an infringement has taken place, based upon things like the originality of the photo or "fair use".
If the board was exported to STEP, then the STEP file is distributed with the project, I think the STEP file has a copy of the original models, so that would be a derived work. The copyright then depends on the owner of the included models.
Usually, if there is any doubt about original material from a copyright owner being included in a derived work, there is an explicit disclaimer. So in the case of compilers like gcc, or fonts, there are specific waivers to allow material to be included in a derived work. Ultra Librarian (EMA) make no such provisions in their formal Terms and Conditions, so the safe interpretation is that they may claim copyright on derived works.
Considering that the "free" data offered is not even very good, it just doesn't seem worth the risk of tainting an Open Source project. Given the hazy legal grounds and dubious quality, I generally avoid the "free" sites as much as possible.
For hobbyists and SMEs who never intend to publish projects, I guess it is fine, but take note of clauses 3 & 4
You further agree to take all reasonable steps and to exercise due diligence to protect the Software or Content and the accompanying materials from unauthorized reproduction, publication or distribution.
EMA reserves the right to terminate your license and to seek any other legal remedies upon default by you of this Agreement.
If you are careless with their data, and someone gets hold of it, they can sue you for damages. This "free" stuff comes with a lot of strings attached!