It's a cool project but it's not open-source. CC BY-NC-SA is not an open-source license, since it limits what the users can do with the code. This is openwashing.
[0] https://github.com/FindMyCat/engineering-docs/blob/main/LICE...
“Completely Open-Source? What’s the catch?
Yup. No catch. All Software and Hardware files can be found in the Engineering section and the Github page under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License”.
This is in the Frequent Questions section. (You need to click on the question to see the answer.)