I'd argue that they're still open-source because inference code
is fully public. In operation, a user can crack open the model and examine its internal state, and we also see that many people produce various modifications or fine-tunings of public models for their own goals.
In my mind, this meets the conceptual and technical bars of an 'open source' designation. We can also imagine the opposite, where inference itself has to pass via an inscrutable binary blob that keeps the model's technology stack fully proprietary.
You're correct that we're missing the training data, the training recipe/curriculum, and any secret sauce that went into optimization of same, but I don't think that's an essential feature of an open source designation.
Instead, I think that the model weights are a kind of rendered artifact, and it should be evaluated on that basis. We don't treat permissively licensed images as something lesser, even if the photographer or illustrator supplies only the final image rather than the full camera raw file and/or Photoshop layer stack.
The difference, of course, is that the rendered artifact (weight blob) in a language model is so much more important than a typical photograph.