I would say that antique poker chips that are termed "engraved" are made approximately the same way that modern casino chips are made with a "mold". The engraving is done on the die that compresses the clay leaving an incuse image. The image is then usually filled with colored paint. Old poker chips are not normally hot-stamped, but can be as in the example shown where additional images are stamped into the clay inside the carlo design.

RobertE can probably add some more to this explanation, but the main point I wanted to make is that most of the old poker chips you see that are termed "engraved" are not produced by the hot stamp process.