https://app.hncompanion.com/item?id=46962996
This post has 500+ comments with various viewpoints and you see the summary on the right side.
You are right that most of the time threads are organized into local groups. But in the above example, there are many comments that relate to the same topic, but are not under the same parent comment. HN Companion's summary surfaces this into a topic "Limitations of Current AI Models" which shows comments from up and down the post.
You can click on the author name in that topic in the summary panel, it will take you directly to the comment. This is what we meant by "continue the conversation there", i.e you are now in the main HN experience, so you can navigate to child/parent/sibling comments (through the link buttons or keyboard navigation).
We definitely don't want AI to write comments. Happy to elaborate if you need.