[nine_k]

Open source means that you can build from said source.

You can e.g. give away a closed-source game engine with an editor, where you can modify the prebuilt levels, and create your own, to your heart's content. But you can't build it from scratch in a controlled environment, and can't audit it. You also can't do modifications where the level editor interface is not sufficient, e.g. in the renderer. That's not open source, that's freeware.

For ML models, the training set is a crucial part of their source.