The idea is that you might need to invent a new algorithm where a technique from an existing algorithm is used in a modified way or in a new setting, and then k

The idea is that you might need to invent a new algorithm where a technique from an existing algorithm is used in a modified way or in a new setting, and then knowing the actual technique can be essential to find an inspiration. E.g. if you know that convex hulls can be computed by sorting by angle and sweeping, then you might come up with the idea of sorting by angle and sweeping in problems that are unrelated to convex hulls (e.g. determining what is visible from a given point in an environment with obstacles). In general, if you know a lot of those techniques and heuristics, you will be much more effective at problem solving in domains where these techniques apply. It is relatively rare for this to be a big factor in routine software development, so that's probably something one should filter for only if interviewing for roles where you might need to design novel algorithms (which Google probably has more than the average company).