What it means though is that nobody in the community can sell upgrades to the printer, sell spare parts, or, and by far most importantly, nobody can develop a fully open source printhead for this printer to sell.

Right now they are using a proprietary print head from a normal printer (understandably because it is by far the most complex engineering piece and is very complicated). However, an external team that wants to make an open hardware project taking on that engineering challenge with more expertise than this team will not be able to be compensated for their work if they make it specifically for this open source printer. According to my understanding of the license.