Trivia: The topic of xenophobia runs strongly throughout the film. This is a very real issue for South Africa as evidenced by the xenophobic violence in early 2008 where approx. 30 foreigners living in South Africa were murdered and hundreds left injured and/or destitute. In fact there are still displaced foreigners living in homeless shelters, churches, etc today.
Trivia: There have been protests against the alleged stereotyping of Nigerians in the movie. Two of the more sensitive issues are the Nigerian prostitutes soliciting 'prawn' customers; and the character name Obesandjo (which is closely linked to the former Nigerian President's name Olusegun Obasanjo).
Trivia: The 'prawn' design is based on an actual giant cricket species, the mole cricket, found in suburbs of Johannesburg. Commonly known as 'Parktown Prawns', they can grow up to 20cm (8in) in length.
Trivia: The alien languages and sounds were created by rubbing pumpkins together.
Answer: This isn't actually remotely uncommon. Trailers are almost invariably released before the final edit for a movie is locked in place, so it's not at all unusual for shots in the trailer to be from scenes that ultimately don't make it into the finished product, or to be from alternate takes of scenes that do appear. As to why this particular scene was rejected, who knows, most likely was just for pacing, or they might simply have not liked some aspect of the acting or whatever.
Tailkinker