Op, Based on my research on their website, services provided by JLCPCB include (1) PCB fabrication, (2) PCB assembly and (3) 3D printing and CNC. I might miss something but you got an idea. So essentially they are a service provider who receives the design file uploaded by DIYers and fabricate PCB for them, with an option to assemble components provided by LCSC on the PCB. They do not verify if the uploaded design files are legit, free of infringement of someone’s IP, nor do they own the design after manufacturing. They simply fabricate / assembly PCB according to the DIYers’ request.
I am not a DIYer, so I don’t have knowledge of the general practices or ethical codes in the DIY community. You could possibly advise the general audience here about that if you belong to the community.

