Electricity was discovered around 600 bc, electric eels weren’t discovered til the 1740s (named in 1766). Natives in South America likely interacted with them, but we don’t have any records of what they called them. Most likely though we would’ve named them something to do with lightning if we hadn’t figured out electricity when we found them.
Unfortunately, your article was pretty lazily written. IDK how they even got away with it. It took me about 5 seconds of googling to find that indigenous people in Venezuela called them "Arimna" or “something that deprives you of motion.”
I love how things aren't "discovered" until white people see em. Even though like you pointed out, humans who actually lived in those regions were very well aware of them
Things are only discovered until documented and the information spread, it has nothing to do with race. In the same way Adam Savage said "the only difference between screwing around and science is writing it down"
This /r/AskHistorians post has a nice discussion on it. While there's little in the way of records for precolonial South American names for it, one person has found the example of arimna, "that which deprives of motion".