Old thread just appeared in bold near the top of my "Latest" listing. Why?

This thread appears to have no changes for over a year:

So why did it just appear in my “Latest” listing?

Another one: Comments and Reviews in the 3D Warehouse

And another one: Windows 10 comments

Spammers commented on these threads. Although the comments were deleted (as they were spam), I guess that still counts as a new comment, so the tread shows up as having been updated.