Well, we don't go around locking every thread that's over a month old. Yes, the rule is that you can't post in it if it is over a month since it's last been posted in, but generally speaking this is overlooked if the OP posts in it after a month (providing the post in question is of significance). So a month-old thread will be locked if the owner so wishes, but is still not to be posted in otherwise by anyone other than the OP.
(in this case, Hiroshi Sotomura could lock it himself if he wanted to, being a Higher Staff member).