Light meters are calibrated to reproduce subjects as middle grey.
Some manufacturers veer slightly from that standard.
Your light meter and camera are conspiring to reproduce everything as middle gray. The meter has no way of knowing whether it is pointed at a light area or a dark area. The Zone System uses this bit of understanding to build a set of tools which allow you to soar into new regions of photographic control. So if you want to reproduce something as middle gray, there is a chance it will work. First point your meter at the subject you want to be middle gray, meter on it, then use the indicated reading.