The author has actually managed to write this nameless MC to be smarter than 99% of isekai main characters, including those that got hundreds or thousands of points in intelligence (depending on the scale). He's not necessarily acting super smart in his everyday interactions with people, but when it really counts, he does control his behavior and words finely. But then again, even if his behavior in normal situations may be clumsy or nearly rude, it also help to lower people's expectations, which makes things easier for him. Things being easier is his primary goal, after all.