I see, so perhaps it wasn't a question, but a snarky remark. Still not sure... Assuming it was a question, yes it's nature. The subtopic, presumably, was the following:
> metalo, karbo, fero, elektro, densa, flue, formo, konsisti, truo
Electricity is part of nature, and so this doesn't seem too much of a stretch. Either way, he/she is learning Esperanto with the sentence, right?
It's a completely reasonable confusion and there's no need to be defensive. Yes, it's a minor issue, but nevertheless electricity is not what we associate with "nature" as the word is understood colloquially. Electricity is part of nature, but so is nuclear fusion, yet we probably wouldn't put that under "nature" topic.