Redwood search filter number in brackets - what does it mean?

Summary:

We have been asked what this number appears to mean in some search filter parameters on various pages (example Document records, Employment Info)

Content (please ensure you mask any confidential information):

As above, you can see a number in brackets; however this doesn't seem to translate to people records or assignment numbers within respective departments.

A filter of people with position of 'Senior Lecturer' in the department of Bioengineering shows a list of 15 people.

In the position filter it then says 'Senior Lecturer (15)', but in the department filter it says 'Bioengineering (97)' - if I filtered only by department it's quoting 4353, but when I do a query of the number of people and assignments in this department it's in the order of 700-750. Where is this number coming from?