Possibility: The human brain and GPT-3 are doing radically different things and aren't even comparable. GPT-3 is merely memorizing enough language to pass a turing test, whereas human brains are actually learning how to use language to communicate with other humans.
Evidence: Have GPT-3 write your work emails for a day, and then live with the consequences of that for the next week. It's going to produce text that makes sense, but only in a very particular way. You will end up with email threads where an outsider says "yeah looks like work emails. I believe this is two humans" And, that's very impressive! But your actual interlocutor who understands the full context of the conversation and relationship will legitimately worry for your mental health and maybe even contact your manager.
Conclusions:
1. Any time you invent a test, people will find ways to pass the test with flying colors but completely miss the point of the test. The turing test is no different.
2. Being able to imitate a human well enough in a five minute general english conversation is only so useful. There's a reason we don't pay people living wages to write internet comments. This isn't to say that GPT-3 is useless, though. There is certainly demand for very specialized five minute conversers that come at zero marginal cost. I'm worried.
3. We still have no clue how to even begin to approach AGI.