It's IMO a pedantic distinction.

A compiled binary is a bad metaphor because it gives the implication that Mistral-7B is an as-is WYSIWIG project that's not easily modifiable. In contrast, there have been a bunch of new powerful new models created by modifying or finetuning Mistral-7B such as Zephyr-7B: https://huggingface.co/HuggingFaceH4/zephyr-7b-beta

The better analogy to Mistral-7B is something like modding Minecraft or Skyrim: although those games are closed source themselves, it has enabled innovations which helps the open-source community directly.

It would be nice to have fully open-source methodologies but lacking them isn't an inherent disqualifier.