IMHO "open source" is not the right term for this because, besides sounding like it was created by people with a software-centric view, it legitimises the application of Imaginary Property laws to physical objects --- something that is a relatively recent phenomenon and one that I think should not continue. Perhaps "open design" or similar would be more representative of the intent.
For example, the automotive aftermarket is so prolific and complete that you can build an entire stereotypical mid-century car with entirely aftermarket parts, but I wouldn't call that "open source". People have also been making tractors out of car parts for a long time (there are some old magazines with plans for such), as well as fixing heavy equipment by making their own parts --- look at various YouTube channels for examples; and I don't think any of this is comparable, nor should it be, to the quagmire of IP laws that the software world is subjected to.
tl;dr: Good intent, bad naming and perhaps some ignorance of how the physical hardware world operates.
It's not just that, it's a deliberate dig against the current trend of farm equipment mired in opaque binaries, DRM, and OEM sensors, that require an OEM service tech to fix. Not for any mechanical reason, but because they restrict the diagnostic software.
For example, the automotive aftermarket is so prolific and complete that you can build an entire stereotypical mid-century car with entirely aftermarket parts, but I wouldn't call that "open source". People have also been making tractors out of car parts for a long time (there are some old magazines with plans for such), as well as fixing heavy equipment by making their own parts --- look at various YouTube channels for examples; and I don't think any of this is comparable, nor should it be, to the quagmire of IP laws that the software world is subjected to.
tl;dr: Good intent, bad naming and perhaps some ignorance of how the physical hardware world operates.