Yes, the trained model is too complex to understand. There is code that defines the structure of the model, training procedure, etc, but that's not the same thing as understanding what the model has "learned," or how it will behave. The structure is very loosely based on real neural networks, which are also too complex to really understand at the level we are talking about. These ANNs are just smaller, with only billions of connections. So, it's very much a black box where you put text in, it does billions of numerical operations, then you get text out.