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.
That's what those hackers do. They no longer change passwords so that the owner of the account won't be alert through their email address that the password has been changed. All they do is log into the compromised account and the post links to malware
If the owner of the account or the mods are not attentive enough, this can appear as though the real own of the account made such a post.
Anyway, good luck to Harizen on recovering his account and perhaps a reminder to use stronger passwords, different passwords for different sites and avoid malicious apps or browser extensions on his device.