Yes, that was a sort of mistake. The first mistake was that many years ago the original Modiying values in html form was posted in Categorized Questions and Answers when it really should have been posted to Seekers of Perl Wisdom. The second mistake was that it went unnoticed for many years -- ideally the Q&A Editors would have noticed and kicked it back to SoPW years ago.

Then a day ago the answer you linked to, Re: Modiying values in html form showed up, drawing attention to the original parent node, and someone from QandAEditors had the good intentions of using the Q&A Editors' "SOPWify" tool to toss the thread out of Categorized Q&A, since it really was a better fit for SoPW. Unfortunately that person SOPWified the followup, not the entire thread. Some of these tools are a little clunky, and since they're not used all that often, it's easy to make a mistake.

At this point it's probably best to just SOPWify the thread, and then to reparent the follow-up under it using the Janitors standard set of tools. I'll see if I can kludge my way through it without making it worse than that person already did. ;)

Update: Alright, that's taken care of. The original node, which really was asking a question, not presenting a Q&A style discussion, has been moved to SoPW, and the follow-up has been reparented under the original, where it belongs.