Even if I agree that it wasn't really necessary to clean up an old topic, these multiple posts have probably been reported. Who is to blame ? The mod or the person who reported them ?
If the mod hadn't done anything, we would have seen messages saying: "it's a scandal, my reports have not been handled or marked as bad !!!"
And from what I can see in the topic you linked, the multiple posts of several members have been merged into a single post.
So, is it really a big deal ?