Deliberate mistake: The atmosphere on Mars is only 1% as dense of that as Earth, so 175kph windstorms would feel like a light breeze. They would have very little effect on the astronauts or MAV. The writers of the book and the film were aware of this, it was a small cheat to let the rest of the story unfold.
Deliberate mistake: The little red-haired girl boards a bus with other children who are headed to summer camp. As the bus drives away, there is nobody in the driver's seat. This movie maintains Charles Schulz's policy of never showing adults in his comic strips or animated television specials, but a bus driver could at least have been depicted in silhouette.
Deliberate mistake: If the files on the hard drive are encrypted, as stated, they would also be locked against being deleted by a command, and Atlee would not be able to use a phone in close proximity to issue the delete command. He would need a massively powerful magnet or EMP to clear the drive.
Deliberate mistake: At about 1:49 in the movie, Glass is awakened by an attacking force of Arikara, and he fires his single-shot, muzzle-loading flintlock pistol at the nearest one coming at him. Then he runs to his nearby horse and flees, turning back to fire the gun a second time immediately. No reloading and no second gun on his person. It never leaves his hand; he's whacking the horse's rump with it to goad it on as soon as he jumps on it. And then he fires that same gun another time in a matter of seconds. (01:40:00)