That's not uncommon or unexpected.

Many decades ago I worked at the sierra natural history museum in california. It on a college campus and it has a Richter scale within the confines of the museum

Classes more or less released for lunch at the same time every day past a certain point due to teachers union agreements. The Richter scale would always register a seismic event just from students migrating from the classrooms to the various food venues and seating areas. We had to make a note on the printout (yes I'm that old)