He's updating the links for his pictures. This will cause the post to get updated and therefore show up as a new active post. I expect that Bill-n-Donna's pictures have been moved to a new location on the internet which would then cause the forum links not to work and he's fixing them.
FYI - if anyone changes any post, the forum will consider it a "new" update to the topic and revive it as a new active topic. If you are curious, sometimes it's not a new response that causes the topic to get re-activated (aka "bumped"), so it might require a check of ALL the posts in the topic to find what entry was edited. In Bill-n-Donna's case look for their posts that include pictures.
I hope this helps.