It's an old adage. But it's less smart than it sounds [1]. Swimming is an action defined by its mechanics- you swim when you do certain precise movements with your body. Understanding (or thinking, in the original formulation) is a process that is defined by its consequences. The consequences of understanding are simply that you respond in an appropriate way to the original stimulus with speech or actions. To go back to the original metaphor, it's not about the specific movements of swimming, it's about going from point A to point B in water. And yes, submarines can do it. And yes, GPT-3 seems to understand a lot, in that it responds to a lot of inputs in a meaningful way.
[1] Take that, Dijkstra!
AI systems could affect large aspects of society. We should be clear about their limitations, and not be swept away by hype.
Being so different and yet so similar, it's maddening not to know whether they're converging, or if it's a dead end, or even if it's going in some entirely third direction.
The fact is, it is more general-purpose, and generates text that is much more coherent than what we've had before. Decade or two ago even that level of apparent comprehension was science fiction.