Note that it says "interactive software application" not "website", though it's possible on a website using a single page application and preloaded resources. Any time you're fetching a resource from some external source, it's unreasonable to expect it to load in under 64ms.

I assume the intention isn't speed alone, but part of the user experience. When you interact with an application, you should be able to tell immediately that it's recognized your input and something is happening.