@dataminded explained it pretty well, at least based on my experience. I'm not on the HR/hiring manager side of this one (technically a separate team I collaborate with), so I can only say that it does appear that it is the desired years of experience for this particular role.
Having worked for a number of years in both the private and public sectors, I can say that job titles and descriptions do not necessarily always align between the two. In other words, I understand what you're saying, and can empathize with your confusion.
If helpful, the job descriptions/classifications for all roles at the City of Minneapolis are available online:
In this example, it's a bit different as in it is known across the industry.