Ok now that's chinese for me....
What do you mean by "cast"?
I think he means the metal is cast, like cast iron, where hot metal is poured into a mold. I have never even heard of that for files of any sort, but many manufacturers do run blanks through a rolling jig to cut/ raise the teeth, which is not as good as somone cutting the teeth in by hand onto the annealed blank, and then heating and quenching the steel to harden it. I don't klnow manufacturers by reputation for farriers rasps. I just bought what they had at the seed and feed store, 15.00 and it was great.
You might want to look into the "shinto" rasps, too. A very clever design, and not too expensive. Ebay has some, last I looked.