I closed the post. The flag being addressed at the time was that it was "off topic, it belongs on Server Fault".
As Michael Petrotta said, nginx is a server application/admin tool/etc.
With that in mind, these questions are tricky, as there's no clearly defined point for when it becomes about administering/configuring the server/application through script (off topic), or programming against the server through the same scripting interface (on topic).
The fact that it's Lua doesn't make it any easier.
The former is how I viewed the question, hence the reason for the off topic closing.
I hope that this has not hindered you or given you a bad experience with the site, that is definitely not the intention, nor was it viewed as horribly inappropriate for StackOverflow, it simply was a judgement call, one that I apologize for.
As for why it wasn't migrated, again, as Michael Petrotta said, you don't want to migrate crap, so these questions don't get migrated instantly just because they are considered OT.