While looking at the grid I see that Mike posted the last comment. But when I navigate into the topic his post is not visible. I suspect is was deleted and the grid does not account for that. If so that seems kind of weird.
Discussion posts and replies are publicly visible
Thanks for reporting this. As Mike mentioned there was a spam comment and a few replies that were deleted. Currently, the grid view doesn't reflect this update and still records Mike has having the last comment on the post. Our team will need to look into this further to see if there is a way to have the grid view refreshed.
I know you guys have very limited control over the Community forum software (if any), but there's a threaded comment board technique used elsewhere that handles this situation pretty well: when a comment is removed due to abuse/spam, a placeholder is still seen with text saying "[deleted]" or similar, and threaded (unremoved) replies still appear below it as normal.