Nope, threads never close automatically. Maybe your thread was closed by a Mod.

It was probably closed because you both started the thread and made three consecutive posts at the end of it, which looks like you're bumping an old thread nobody else cares about anymore.

Now, I know the kind of guy you are, and I know you weren't... but it was undoubtedly closed by a mod because the pattern looked suspicious.

That makes sense. I didn't intend to do that, but agree that it is best to implement measures to discourage such a practice. Come to think of it, some of the things I've been doing here do look kind of suspicious, lol.