The key word is "occasionally". For anything even close to AGI, it would be reasonable to expect a correct answer to such a simple question 100% of the time. Or at least not confidently wrong answers.
The question the paper claims to address isn't whether current LLMs are AGI, the question is whether LLMs can reason. And solving a problem that seems to require reasoning some of the time is still evidence of reasoning - especially if the question is what we can expect this technology to do in the future.