Scaling down and scaling up are two very different problems. It isn't a given that scaling up is a harder problem than scaling down, it rather depends how far

Scaling down and scaling up are two very different problems. It isn't a given that scaling up is a harder problem than scaling down, it rather depends how far down and how far up. If they were looking for a "subject matter expert", rather than someone who could become a SME then failing the interview is entirely expected. The techniques for scaling down are unrelated at best and at worst totally the opposite of the techniques used for scaling up.