Does anyone actually decide, "All right, I'm going to write a superhero story?" As the first thing? Except, of course, a hack trying to grind out a novel before the wolves decide hanging out at the door is too dull, they will jump in the window. But the advice doesn't read like its target audience is meant to be hacks.
I generally figure out the genre from the thing I start with. I have a scene. I have a cool meta origin. I have a villain. I have a cool curse. I have a beef with a popular but incoherent superhero trope. Sometimes the starting idea is not sufficient to dictate genre, but then it meets another and the story crystallizes about them both. The more abstract an idea is, the harder, but I can manage because it's never so abstract as "A superhero novel."
It really does make me wonder whether anyone does write like that.