I'm torn between interpreting this as NPCs being NPCs and people just being really horrible at estimating using numbers.

Have you ever once seen any statistic at all where the general public was good at estimating it? Even something as simple as estimating lengths of time. I can't tell you how many times someone has described a two second interval as "half a minute", which would make them off by more than a factor of fifteen. Almost everyone I know does it.

Or how about a topical issue, the gas crisis? Every time gas goes up, there's a surge of new Prius buyers, even though if gas went from $2 to $8 and stayed there permanently, an average person would only be saving like $200 a month on gas, which means it would take over 12 years to break even.

Never trust an untrained person to be able to process numbers.