Yes, I tested this on my own self-hosted Discourse site and it looks like you are correct. Replying to the “about this {category}” topic does not bump the topic into latest.
I checked in anonymous and logged in user mode and confirmed, the “about this {category}” topic is not bumped to latest on new reply in either case.
I can’t quite recall why that would be.. perhaps because it is a pinned topic that has become unpinned on read to end? 