A big difference is that the expert asks different questions, off in the tails of the distribution, and that's where these LLMs are no good. If you want a canonical example of something, the median pattern, it's great. As the ask heads out of the input data distribution the generalization ability is weak. Generative AI is good at interpolation and translation, it is not good with novelty.
(Expert and know-nothing context dependent here.)
One example: I use ChatGPT frequently to create Ruby scripts for this and that in personal projects. Frequently they need to call out other tools. ChatGPT 4 consistently fails to properly (and safely!) quote arguments. It loves the single-argument version of system which uses the shell. When you ask it to consider quoting arguments, it starts inserting escaped quotes, which is still unsafe (what if the interpolated variable contains a quote in its name). If you keep pushing, it might pull out Shell.escape or whatever it is.
I assume it reproduces the basic bugs that the median example code on the internet does. And 99% of everything being crap, that stuff is pretty low quality, only to be used as an inspiration or a clue as to how to approach something.