Stolid is an adjective that means not easily moved.
Don’t be misled by out word of the day’s origin. It comes from the Latin stolidus (STOW lee doos) which means stupid. But a stolid person isn’t necessarily lacking in intelligence. Instead it referred to people who appear stupid because they say nothing. More recently the word has shed any connection to stupidly and is more likely to be used as a synonym of ‘unemotional’ or ‘stoic.’
Kevin’s demeanor remained stolid throughout the movie. I got the impression that he wasn’t moved by it at all.