I suspect the task was specifically designed to give Siavash his moment to shine. Did you notice how confident he was just before he started wrestling with Marcus? I'd bet money that he has wrestling experience and that BB knew that from the interview process:
http://en.wikipedia.org/wiki/Kırkpın...stling_in_Iran
http://en.wikipedia.org/wiki/Iranian_Wrestling
If so, it might have been nice of him to mention it to the other HMs. But I suppose we don't know for sure.
But as I say. I'd bet money on it