Could some of it be explained by demographic changes (immigration)? iI remember always being taught growing up than 37.5°C was the average human body temperatur

Could some of it be explained by demographic changes (immigration)? iI remember always being taught growing up than 37.5°C was the average human body temperature. However after moving to East Asia I met plenty of people who consider 37.5 a light fever and 36 the normal temp. On my phone so no data to back it up for now though...