There's mixed scientific consensus on the full impact of nuclear winter. This paper shows evidence that it would be really bad (in the sense of several billion dead).
As I understand it, the contention with the nuclear winter hypothesis is not whether a ton of soot in the atmosphere would wreck the climate, but rather whether a nuclear war would actually loft that amount of soot into the stratosphere.
And this study suggests it would, in fact, loft a lot of soot into the stratosphere.
To my reading, no. That's not the question the study is addressing. The study is examining the climate impact of six soot-injection scenarios, not the premise of soot injection itself. It cites other papers (some modern, some from the 80s) to justify the six soot-injection scenarios considered, but this study is about applying climate models to those scenarios.