For large volume, good quality text and graphic images in the early 50s, the newest best process was phototypesetting, images and text of the same color were arranged and photographed to produce an image carrier for each color. Pretty much the same as color ads in magazines until the newer computer processes took over in the 90s... The only better printing would be gravure (intaglio) which produces raised ink like you would find on invitations, business cards, and money.
The photomechanical processes produce 'dots' because the plates have various sized holes that carry the ink, but the dots are not in line like a dot matrix printer, the youngster writing that one story I glanced at that you posted is an idiot. The magazine 'print' of the painting is a multi-screen photomechanical process, which is exactly what I would expect to see on old docs with graphics printed in the thousands of copies. If THAT old document were scanned and then printed with a modern inkjet process, the color dots would be run together more by the scanning and then pixelated by the printing process, and would show distinct lines and square edges that your document doesn't display.