The initial claim of the Atlanta Journal's article is that "It would likely take anywhere from 50-100 cups of coffee to result in a lethal dose of caffeine."
This statement was made by Dr Robert Glatter in an interview with USA Today about the lethal dose of caffeine. Glatter is a trusted source in the medical field whose credentials have been verified as recently as this October in a Forbes article which stated the following credentials, "Dr. Robert Glatter, an emergency physician on staff at Lenox Hill Hospital in New York City."
The article further enforces its claim by citing information from the FDA regarding safe dosages of caffein for the average person, "400 milligrams a day... [or] two to three 12-fluid-ounce cups of coffee." In excess of this amount some people may begin to feel adverse effects.
In summary, the original claim, “Here’s how much caffeine it takes to kill you” is true, the article provides readers with statistically supported information for excessive and safe amounts of caffeine intake. In addition, the sub-claim that it takes "50-100 cups of coffee to result in a lethal dose" is also corroborated by reputable sources such as physicians and the FDA.