If I write a program, then obfuscate it and then release the obfuscated code under an open source license, would you consider it open source(I would)? That's kind of the case here, they are releasing the model weights under an open source license.
Personally, I think it's fine to shorten it to "open source model" instead of "a model with the weights released under an open source license". What I would object to is releasing model weights under a restrictive license and calling that open source.
I wouldn't. Most definitions of open source say something like "in the form used for editing". You can release a built binary under an unrestrictive license, but that does not mean that you've opened the source. It's literally the plain meaning of the words: the source, as in where the thing comes from, needs to be open for it be meaningful.