The University of Cologne has a rather high number of students that are only enrolled there for the Semesterticket (public transportation ticket valid in most of North-Rhine Westfalia) and as such, the official number is slightly below 50000 students if I recall correctly.
Compared to that, the 100 students are just 0,2%. The number of "active" students is around 20k I think - so the ratio is still significantly below 1%
To be fair, it's impossible to get anything close to resembling the NRW Ticket (flat fee for unlimited use of regional public transit in all of North-Rhine Westphalia) as a non-student.
The closest equivalents are either offered by the local public transit unions (which are limited to the region covered by that public transit union, of which there are a ton in NRW) or the BahnCard 100 (which covers all of Germany -- but not necessarily all local public transit -- and is ridiculously expensive).
