You're fucking stupid, that doesn't mean he doesn't know what it means to be a hero, it means he wanted to explore that topic. Here's what he actually said:
WHAT IS A HERO?
Interviewer: This subject is present in the current arc, but for Horikoshi-sensei, what is a Hero in Boku No Hero Academia?
Horikoshi: “What exactly is a hero?” This is what I think about and what makes me want to draw. What is a hero? It’s hard to put it in words.
Interviewer: How would you define the image of a hero?
Horikoshi: Moreso than that, I personally do not want to define that. When Boku No Hero Academia first started, in a past interview, I remember answering “A hero would probably have this type of existence.” Recently though, I have been thinking about how there’s way more viewpoints that correlate with what is a hero. For example, some people might think a hero is someone who “even if they’re a lone wolf, they would still do their best, and that’s what you can call a hero.” There are also others who might think that heroes would be like a pro baseball player, someone who hopes to let everyone enjoy their work. There’s no single word that can pinpoint “Ah, this is a hero” in my opinion.
Interviewer: Has there been any triggers that made your own thought process change within the story?
Horikoshi: As the serialization continued, and after seeing various reviews from readers, I decided to start moving various characters’ stories forward. For example, for Deku, a hero is someone who can save people, and for Katsuki, a hero is someone who can win. When I realized that I had to write about their entire stories, I started to think that I had to figure out collectively what a hero figure would be for various people, and I guess if you call that a trigger, then I guess it is one.