Well, in the case of a thread about Anderson's english, it should not be merged in the "all things anderson vs. chael" thread.
The only threads that should be merged into such a thread, is all threads regarding Anderson vs. Chael. The thing is, that means ALL threads regarding Anderson vs. Chael. That means, if a thread is made that is called "can chael take anderson down?" that thread gets merged into the big A vs. C thread.
I don't really recall the Anderson english thread you are talking about, but the only reason why I could see it being merged is if the thread turned into a Anderson vs. Chael debate (many threads go from one topic to the next, happens all the time), or if the thread was about how Chael said Anderson could talk english and how he's going to beat him up, which starts the "well, anderson will destroy chael" and so on, so forth, and would be merged.
If neither happened, then yeah, it shouldn't have been merged and I would have no clue why it would be merged.