OP here. I think this is exactly right "The exact number is irrelevant, the fact that there is a number is relevant. That means the developer not only understood the business requirements but also measured the impact afterwards."

In follow-up interviews, the interviewer may dig into those results, and in reference checks, may try to confirm your achievements, so I do not think it's accurate to say it would be OK to use BS numbers.

But the overall sense that numbers are important, and send an important signal about a developer's work habits, patterns and practices, is true.