[pessimist]

ChatGPT understands what it reads. In the sense that it is actually creating a model of what it just read, and it's own output. It happens to understand English, dozens of programming languages and perhaps others. There is no other explanation.

It often makes mistakes, and that's the only reason why it's currently inferior to the human brain.

Surely it be writing full fledged correct programs in under 2 years.