I actually meant to present that as: Because I didn't flip the switch.
A counterfactual requires posing a situation with changed facts. I stand by my statement, saying "X because not Y" is not a counterfactual on its own. "not Y" is still a (potentially) factual statement. And guesses still aren't counterfactuals. "Maybe the lights aren't on because we didn't flip the switch?" That's a hypothesis, and a testable one. Still not a counterfactual. If we know the flip hasn't been switched, then it's just a fact even if the statement is in the form of not X.
The counterfactual is "if I had flipped the switch, the lights would be on." That is a situation with changed facts, and therefore counterfactual. The tricky bit is the causality. We have to construct an alternate history, with a counterfactual cause and a counterfactual result. And we can't actually know that. Maybe the bulb is burnt out. Maybe there's a power outage just now. Maybe we've blown a fuse. The causality is just conjecture.
Now consider the opposite. The lights are off because the bulb burnt out. That's a lot less ambiguous. If you want to doubt the causality you've got to get all mystical.
But no, in a meaningful sense it's not a true statement about the world. It's a good guess, and for a statement that simple, there might be no need to go further. For a statement about why a volume is full with too many files, the point is that a nice-sounding "if only" isn't something you can test or be certain of.
Your answer about blind people is a very good guess as well, and the same one I would make, but it's not data.