Maybe someone can tell what type of typewriter he used, but it's clear that Bierce was comfortable using one. He even makes a typo by omitting a word. That makes me feel good. I am sure that by 1911 using using a typewriter to write wasn't that unusual. But not many authors were embedded in Panco Villa's army in Mexico.
Mexico was a land of Olivers. Especially, Olivers that are nickle-plated. Like this typewriter from the poet Ramon Lopez Velarde. (Fun lit fact: Octavio Paz studied Velarde and wrote a great deal about his influence in post-modern mexican poetry.)
Oliver realized that Mexico had been overlooked in the market and sent a man by the name of Parker to change that. Parker was able to introduce the country to the typewriter and the Oliver. At this point in 1911 if you wanted to buy a typewriter in Mexico it's likely you were buying an Oliver. They were used in all levels of the post-revolution republic. LC Smith did have some offices, but I think many companies were more concerned over the perceived danger of early republican Mexico. Richard Polt has a blog post about a nickle LC Smith that includes a mention of nickel Olivers.
The mystery is: did Bierce use a nickel Oliver or did was he supplied a typewriter by his American editors? I am going to investigate this information further. It should be interesting whatever I discover.