"I didn't turn them on" is a fact. It's the "because" that's not a fact. The whole point of the article is that you can't get causality from things that didn't happen. There are seven billion other people in the world who also didn't turn on the lights. What makes your inaction special?
In order to get the "because" we have to imagine another state of the world where you DID turn on the lights, and further speculate that this would have been effective to illuminate the room. That's counterfactual, because the fact is that it's dark in here.
In order to get the "because" we have to imagine another state of the world where you DID turn on the lights, and further speculate that this would have been effective to illuminate the room. That's counterfactual, because the fact is that it's dark in here.