The goal of the KiCad 3d model library is to provide a free open library of 3d models. This requires certain restrictions regarding contributions with respect to their legal status.
Users must only submit models for which they own the rights allowing relicensing under the KiCad library licence.
In most cases this means they have created the model themselves, either manually designed in a parametric modeling software or via scripting tools.
Contributing model data designed by a third party complicates licensing issues and is to be avoided. This includes files downloaded from a manufacturers website.