The open source movement, from which the name derives, was about the freedom to make bespoke alterations to the software you choose to run. Provided you have reasonably widespread proficiency in industry standard tools, you can take something that's open source, modify that source, and rebuild/redeploy/reinterpret/re-whatever to make it behave the way that you want or need it to behave.

This is in contrast to a compiled binary or obfuscated source image, where alteration may be possible with extraordinairy skill and effort but is not expected and possibly even specirically discouraged.

In this sense, weights are entirely like those compiler binaries or obfuscated sources rather than the source code usually associated with "open source"

To be "open source" we would want LLM's where one might be able to manipulate the original training data or training algorithm to produce a set of weights more suited to one's own desires and needs.

Facebook isn't giving us that yet, and very probably can't. They're just trading on the weird boundary state of the term "open source" -- it still carries prestige and garners good will from its original techno-populist ideals, but is so diluted by twenty years of naive consumers who just take it to mean "I don't have to pay to use this" that the prestige and good will is now misplaced.