Other mistake: After they blow up the dam blocking their passage, there is a far away shot as they are going up river and there's a grassy landmass that goes across the river blocking their route up river.
Continuity mistake: Jennifer Lopez's eyebrows go from sparse to filled in in several scenes.
Continuity mistake: Serone catches a fish using a spear and then chops it up with a knife and a mallet. He then talks to the crew about their documentary and walks back to the chopping board where he proceeds to chop the same fish again, which is now whole. (00:12:32 - 00:13:21)
Answer: They didn't set it up. They were chasing after the anaconda anyway and were stranded. They still wanted to go after the anaconda after they were picked up, so they lied to the crew. They knew the crew wouldn't go after the anaconda on their own.