The weights are, for all practical purposes, source code in their own right. The GPL defines "source code" as "the preferred form of the work for making modifications to it". Almost no one would be capable of reproducing them even if given the source + data. At the same time, the weights are exactly what you need for the one type of modification that's within reach of most people: fine-tuning. That they didn't release the surrounding code that produced this "source" isn't that much different than a company releasing a library but not their whole software stack.
I'd argue that "source" vs "weights" is a dangerous distraction from the far more insidious word in "open source" when used to refer to the Llama license: "open".
The Llama 3.1 license [0] specifically forbids its use by very large organizations, by militaries, and by nuclear industries. It also contains a long list of forbidden use cases. This specific list sounds very reasonable to me on its face, but having a list of specific groups of people or fields of endeavor who are banned from participating runs counter to the spirit of open source and opens up the possibility that new "open" licenses come out with different lists of forbidden uses that sound less reasonable.
To be clear, I'm totally fine with them having those terms in their license, but I'm uncomfortable with setting the precedent of embracing the word "open" for it.
Llama is "nearly-open source". That's good enough for me to be able to use it for what I want, but the word "open" is the one that should be called out. "Source" is fine.
[0] https://github.com/meta-llama/llama-models/blob/main/models/...