alt Hacker News> what it actually means is that we don't know enough to say one way or the other.
To take another illustration: nobody can prove that there is not between the Earth and Mars a china teapot revolving in an elliptical orbit, but nobody thinks this sufficiently likely to be taken into account in practice. I think the leukemia claim just as likely.
If there was a teapot at a proposed orbit then there would be various falsifiable ways to prove it one way or the other. Once you do the experiment, you have the evidence. Before you do the experiment, you don't.
If there is a cancer risk then good evidence either way would require randomized controlled trials, which for long-term exposure are very expensive and take a long time, so then nobody does them and nobody really knows the answer. This is not the same thing as knowing it to be false.