Small action posts don’t change the activity date (so closed or unlisted topics aren’t bumped just because of that).
- topic created → first activity
- edit on first post → activity date updated
- unlisted → activity date not updated (because small action post)
- edit on first post → activity not updated (because first post is not most recent post)
- …
Yes, that’s what I expect. You can also create a test topic to see if this helps before trying on the real topic.