Clearly Alien technology, stolen from the Aztechs, who invented geometry, and were black!
Seriously, is this clown saying "typesetting machine", of the type that Mark Twain went broke investing in two centuries ago, and couldn't get invented with 1800's tech, much less Medeval tech?
No, I think he's saying that instead of making blocks of raised letters, then clamping them together in a row to make a line of type, he had blocks of *recessed* letters, and individually stamped them into a plate (presumably with a hammer) in order to leave raised letters on the plate. The plate was then used as the printing plate.
The end result would be a manual version of what typesetting machines do automatically, but it would still be manual.