And big wins like that are usually compacted pretty early on. If you can get orders of magnitude improvements left and right, it means that something about the company's management is off.
It's also not a good question for an interview because it's a hard basis for comparisons. Perhaps another candidate knew how to improve the build/deployment pipeline, but he was blocked by political interference. He wouldn't be able to say "I sped up the pipeline 6x.", but he could talk about his plans to do so with a question more oriented to the task, e.g., "How would you build your dream deployment pipeline?"
That's what I mean when I say they're looking for something spectacular. Some people can say they saved their company or made a change with massive ripple effects, which is not necessarily aligned with the technical difficulty of that change and may cause some candidates to elide mention of it entirely, and some people can't make such big assertions, not because they're not skilled enough, but because the opportunity and/or priority wasn't there.
If you want to know about business gains and side effects of technical work, ask "How did your work help your employer?" If you want to know about technical work itself, ask relevant lines of questioning.
Anyway, I think we're basically splitting hairs here. It's just about what level you're choosing to process the question on, and it seems everyone agrees that it's best to take a very superficial interpretation and allow them to inquire further as necessary. I just don't think it's a good interview question.
(One of the other ones I'm more amused than proud of, though, is saving a client ten times the money they paid me because I happened to know about the existence of AWS D2 instances...)
Your concluding point is well-taken, though, because most people don't know how to interview and they're basically asking you to sell yourself for them. But I don't think the question is as problematic under the hood as you're framing it.