Did you, perhaps, not read down in the article (there is an add that appeared when I looked that made it seem the article was over)? I ask because I think he answers those questions.
The second question is answered clearly - the original chalk was calcium carbonate (and white), then blue natural Italian "chalk" of silica and corundum was introduced, and then Hoskins and Spinks came up with their own manufactured chalk with silica, glue, corundum and coloring.
The first is not as clearly answered, but given the chronology, it must have been that the chalk that pre-dates the leather tip was either actually people grinding their cues into the calcium carbonate in the walls or mined calcium carbonate.
Now I have a question of my own. His conclusion is that the blue chalk "proved more popular among players and room owners". But why? My own answer is because traditional blue shows up less on the green cloth than green chalk.