Lucas, now Disney, never gave permission, but they also never acted against it. So that doesn't mean that it doesn't step on any IP toes, but it also doesn't mean that they're okay with it.
Like JD said, the issue is that K3 just straight up copies other people's work. There's no originality or novel designs, it's just stealing the work of others. Clack and Bro both put work into theirs, they sculpted the designs and did all the work. K3 just tosses some clay in the base, stamps it as his, then rips them off and sells them..