“Perfectly calibrated”, not “perfect”. So if all of their predictions were correct, I.e. 20% of their 20% predictions came true etc.
So in this case, someone making all 90% predictions will have an expected score of 0.9×0.1^2 + 0.1×0.9^2 =0.09, while someone making all 80% predictions will have an expected score of 0.8×0.2^2 + 0.2×0.8^2=0.16
In general a lower expected score means your typical prediction was more confident.
“Perfectly calibrated”, not “perfect”. So if all of their predictions were correct, I.e. 20% of their 20% predictions came true etc.
So in this case, someone making all 90% predictions will have an expected score of 0.9×0.1^2 + 0.1×0.9^2 =0.09, while someone making all 80% predictions will have an expected score of 0.8×0.2^2 + 0.2×0.8^2=0.16
In general a lower expected score means your typical prediction was more confident.