Other mistake: It isn't known if Rory was diagnosed with ASD, but some of his behaviors and the two classmates in school making a reference to his "Asperger's" indicate or suggest this is the case. While Rory may have been "faking" some mannerisms in hope that the two bullies would leave him alone, his (hyper) sensitivity to noise (sound) was displayed after school when a dog was barking at Rory. However, Rory did not put his hands over his ears in the ball field despite the loud gunshots close to his ears. (00:51:54)
Other mistake: At the baseball field after Quinn (Rory's dad) slid through the green slime, he only had green slime under his neck on the front of his shirt - none on his pants or back of shirt where expected. (00:52:52 - 00:53:37)
Answer: Well, in the case of Predators, it was violent criminals, mercenaries and military being randomly kidnapped and dumped on an alien planet. From the perspective of humans, it would appear that the criminals and mercenaries had gone missing in a more mundane fashion or simply died. If the Predators were covert about it, the Predator researchers would not be suspicious at all. So it's entirely possible it's canon.