That's sad, not sure what you can do in this situation. seclog does not show any thing like Password change etc to suspect account hack.

That means your password was probably compromised and someone was able to login and post that thread.

Your only chance of getting back your account back is proving that your account was hacked. I guess moderators might not have access to your IP addresses and only theymos have such access. He can verify if that topic was created from some what "different ip/location", and also if your hacker was in your pc then good luck.