It’s been trained to produce valid code, fed millions of examples, and in this case it’s outputting invented syntax. Whether there’s an example in its training data, it’s still a hallucination and shouldn’t have been output since it’s not valid.
To be fair, it is not trained to produce VALID code, it is trained to produce code in the training data. From the language model point of view, it is not hallucination because it is not making up facts outside its training data.