Whether it has any sort of real understanding or not, it does summarise. It produces summaries as well as many other things. It’s just very unreliable, due to a number of shortcomings that might just be fundamental: no real world model, no ability to distinguish between truth and lies, fact and fiction, except statistically, which sometimes results in nonsense. It can misrepresent, leave things out, and sometimes just make stuff up. It does summarise, but it does it poorly and unreliably.