I think you’re charitable. That such a piece of information, from more than half a world away, would make it to a person willing and able to act on it without the reference making its way into any other contemporaneous western sources, is more than just a bit of a stretch
Well, the person (trader) who actually saw it working in Korea might be have been impressed enough to seek out printers in Europe to inform them of the invention.
I agree it is unlikely, but possible.