Note there's a caveat: problems in CS can be reduced to other problems in CS. If we solved SAT, well, no one cares about SAT, but traveling salesman obviously reduces to that.
(disclaimer: I don't think that's what is going on here, I'd have to dig into it more)
They didn’t solve any kind of CS problem. As far as I can tell the problem they solved is “what is this complicated quantum system going to do” by building the complicated quantum system and seeing what it did.
Then they claim it would take a gazillion years to simulate on a conventional computer. Which I’m sure is true.
Really? SAT is the question "I have a set of constraints. Is it possible to obey all of them at once?"
If it were impossible to use that question to answer any other questions, I'm pretty sure there would be a lot of interest anyway.
It's kind of like how a lot of people care about the determinant of a matrix, which is exactly the same question set against a much more restrictive set of possible constraints.
(disclaimer: I don't think that's what is going on here, I'd have to dig into it more)