I just got done with a Microbiology course last term, so I find this fascinating. Many bacteria have evolved to live in even the most inhospitable conditions, from temperatures as high as 350 deg. C to toxic conditions like those in Mono Lake. So, while the term "extremophile" may sound new, it's a pretty common term for Microbiologists and just means an organism that loves the extreme.
You're right, it wasn't found on the ground. It was found in Mono Lake in California. The very first sentence says as much: "The bacterium, found in a California lake, uses the usually poisonous element arsenic in place of phosphorus." The part you're referring to talks about how they researched the microbe in the lab, not creating it. Knowing the bacterium is fastidious, they checked to see if it grew under the arsenic ric conditions, which it did.