The law of demand frames demand as a function of price and utility — demand is monotonically non-decreasing with utility (the more useful it is, the more people want it), and monotonically non-increasing with price (the pricier it is, the less people want it), but e.g. Giffen goods and Veblen goods break the "monotonically non-increasing with price" assumption of the law of demand.
You can add efficiency to that equation — demand is a function of price, utility and efficiency, and it is also monotonically non-increasing efficiency (The less of it you need, the less people want it). If you could get twice as much saltiness from table salt, you'd cut down demand by 50%.
The Jevons paradox is about the cases where demand isn't non-increasing with efficiency, because utility is itself a function of efficiency. Increased efficiency directly lowers demand, but, because it increases utility, it also increases demand indirectly.
The paradox is usually framed as more efficiency -> more demand (because of the intermediate "more utility" step), but the author is framing it in the opposite direction, as less efficiency -> less demand (because of the intermediate "less utility"). I would argue it's just that the paradox works both ways, rather than calling it a "reverse", but that's me.