The architecture can easily be open source - as long as repo is missing just the training data. Just like there are Doom engines that are open source, even though they do not provide WAD files, which are still copyrighted. The code is there, but it is somewhat useless without the data. Analogy is not perfect, but let’s assume it compiles to a single binary containing everything, maps included.
If ID Software gives you a compiled Doom with maps free to use it is freeware. If they open source the engine (they actually did), but do not release the WAD files as open source, the compiled game is not open source - it is still freeware.
It is not complicated really.
CAD. Free solutions compared to commercial ones (SolidWorks, Inventor, Fusion360, Onshape) are like comparing Photoshop to an open source Paint clone.