Well yeah, he needed some sort of catastrophic event to set the rest of the story in motion, and a huge dust storm which forces an evacuation and then separates

Well yeah, he needed some sort of catastrophic event to set the rest of the story in motion, and a huge dust storm which forces an evacuation and then separates Mark Watney from the rest of the crew was just the thing, so he added it although he was fully aware that storms don't work that way on Mars...