I didn't predict it, I'm terrible at predicting, and I didn't care about the movie. I'm just not surprised by it. It's Stephen King, one of his most popular novels. It had a popular mini-series. And everyone loved the trailer and it had national attention. Yeah, the R-rating it a hurdle, but Deadpool was just the year previous.
So popular source material, good marketing, and I'm not surprised it broke out.