That's right, your question originally said adventures but you explicitly said yes to "or RPGs" in the comments as clarification. Then you immediately got 6-8 answers, all RPGs, that were all appropriate to the other question. "Mouse Guard, 4e, etc..." Your clarification led it to be a duplicate; those answers weren't wrong or accidental.
The original question can't be reopened after being merged. Merges move all the answers and their votes over to the other question.
You can cut and paste your paragraph of question about adventures into a new question easily. It'd take less time than crafting a meta question to complain. In fact, it would take less time than a close and discussion and cleanup and reopen. Reopen the same question, just keep it on track to adventures. 30 seconds of work, problem solved.
The other option was to close it and wait, but you had generated a bunch of new good answers legitimately for the duplicate question, so the right thing to do is merge. Otherwise you re-clarify your question and have 6-8 "bad answers," some of which get voted back up due to people being unclear on things.
I understand you weren't there to see it, and that wasn't your intent, but there was a lot of traffic on that question and they were all RPG system answers. There were no adventure answers and none were going to happen; the question had clearly "converted."