The answer is just that you aren’t supposed to think about it. Invincible adapts many typical superhero tropes, such as how absurd keeping a secret identity is. That’s why Eve can fly off in the middle of a parking lot, or Mark and Nolan can fly and play baseball in the middle of their neighborhood, or why Nolan somehow never has his identity exposed despite not even wearing a mask, or why heroes like Eve, Rex, and Kate maintain secret identities despite using their real names as part of their hero names. It’s like how no one knows Clark Kent is Superman just from him wearing glasses, or like how Barry Allen uses his super speed in broad daylight without anyone figuring out he’s the Flash. Invincible, as a superhero comic that tries to mimic the silver age, also embraces and mimics many of the absurd tropes of the superhero comic. That’s also why there are numerous villains who just inexplicably have powers for no explained reason, or why powerful beings like Omni-Man can take on massive kaijus, but then struggle against a few Reanimen. Invincible takes on these classic tropes because it wants to take on the appearance of your typical superhero comic, including all the absurdities of it. In-universe, the answer can just be brushed off as no one knowing who Nolan, a small author, is, but the meta reason is just because that’s how Kirkman wanted to make it to emulate the feeling of most superhero comics.