Apparently it is also part of its system prompt, since otherwise it wouldn't know what the cutoff date is just by feeding it fresher information - it has to be told the date explicitely somewhere.
LLMs are statistical models and simply generate probable sequences of tokens based on a context (very much like sampling from Markov chains) so there is no a priori reason to believe that the cut off date is accurate.
More generally, all output from the model that seems to be model metadata should be assumed to be a hallucination.