I think the argument was that he did precisely that. Yet history paints him as a great inventor (he was, and filed a lot of patents), and most people likely think of him as a "good/nice guy" which he may or may not have been.
Electrocuting dogs, cats, horses, and even an elephant, says a lot more about you as a human being than the person you're trying to discredit by electrocuting dogs, cats, horses, and even an elephant.
"The war of the currents (sometimes called battle of the currents) was a series of events surrounding the introduction of competing electric power transmission systems in the late 1880s and early 1890s." https://en.wikipedia.org/wiki/War_of_the_currents
Electrocuting an Elephant seems to have occurred a decade after the war of currents January 17, 1903.