Why? Many humans have done the same.
We need to stop believing in or expecting any type of “correct” behavior from AI. Read the article @Mwfan1921 linked for insight into why AI behaves the way it does.
In the case of the bibliography, the mistake is expecting accuracy when the model may just have “reasoned” that it needed to produce a list that looked like citations without concern for content, form over function.
Until we figure out how to build the perfect human, AI will behave imperfectly. We can count on that.