In this case it may be ok because we may assume the author looked over the result and agrees with it. They could remove the citation as far as I'm concerned, the same way they don't have to cite their spell checker.

But a summary is a distillation of an understanding.

chatgpt does not understand anything, it is merely pattern-matching against and recomposing other texts.

The only reason the result is even half way sensible is because as of today, most other text that it is matching against and recomposing was written by people who did understand what they were writing and writing about.

So I would perhaps agree that a person using it as part of the process of their own writing is a good use case. But I would not agree that chatgpt can summarize things, and would not say that letting it do the entire job of interpreting and restating is a good use case.