It's no answer at all, and it's certainly not a foregone conclusion. They could easily just blame it on a rogue employee etc, and there is absolutely no reason

It's no answer at all, and it's certainly not a foregone conclusion. They could easily just blame it on a rogue employee etc, and there is absolutely no reason to believe that they would lose business, since competitors would be equally suspect. If they wanted to actually rebut this they could easily say something much stronger such as: "This would be absolutely against company policy, and we have process in place to safeguard against it which we publicly document." The problem is that the search results almost certainly do reflect the company's biases even without any intentional rigging, so they can't answer that way.