Because he doesn't know what the average powerlevel of commoners are because he never asks and other people assume he knows common knowledge because they don't know he's from another world to begin with
He never asked.... but he should have enough intelligence to realize that he's OP....
Like, basic intelligence from watching other people and other people's reactions. Not knowing is only a good excuse when he just barely starts....
Even little kids can understand when they are better than others when there is way too obvious of a gap....
Being ignorant would only work if it's a low key power and the results aren't that much better than everyone else...
I mean, everyone telling him he's so strong and him repeatedly doing sh*t people think is impossible should be a clear indicator...
And if a person with such a large amount of power is still too stupid to understand, then there should be consequences...
Look at the characters from Fairy Tail... dudes causes so much random damage cause they're too stupid to realize how powerful they are...
People get hurt, towns get destroyed and they get scolded and even arrested...