This is the right terminology. Model weights are literally compiled binary data; they are the output of an algorithm run on a bunch of source data. That training dataset is the "source" of the model. Training data (or the scripts used to generate it) is human-readable and modifiable, like source code. Binary weights are not.

I propose that from now on we call freewares "open binaries".

Does an “open source” model the way you describe it exist or is it a mythical creature?

I'm not a lawyer, but I believe that the weights aren't subject to copyright. So, you can use them outside of Meta's license agreement provided you get them from somewhere else.