Not surprising at all. I throw a wall of code at GPT-4, write a paragraph of what i want it to do (I couldn't spend the time to figure out a good solution), and within a minute I had a great functioning solution perfectly integrated into my existing code.
The surprising thing is not that it was able to code a good solution, it's that it was able to understand the specifications of how i wanted it to work and how it should be integrated into the existing code.