Caching is an abstraction, not an optimization

Caching is an optimisation. Sometimes caching can be abstracted away, eg CPU cache or build cache are pretty much abstracted away for a usual web developer. But web page caching is very hard to abstract without any abstraction leaks and weird bugs. And even CPU cache is no longer an abstraction if you deal with very high performance code.

It sounds like they are arguing that when performance matters, you have to know more about caching. Fair enough, you have to know a lot more about things when optimizing. For a lot of cases you can ignore caching because it can be done transparently. You depend on it to some extent because if e.g. every instruction had to be fetched off rotating storage like the old days, it would play a big role in your design. It's just something solved in general for most software to not have to know much about it.