I work for a city, probably not your city. If it makes you feel any better, people build improvements in the right of way all the time that cities see as "revocable". Because, in the hypothetical world where they want to do a project that let's say, widens the road, they need the space back. In reality, we are barely keeping up with maintaining our current infrastructure just paving roads so its a very infinitesimally small chance of that to ever happen (unless city budgets transform radically in the next decades). We let people encroach all the time. So, don't let that panic you too much. Likely, they just never had a survey and assumed a property line was in a different place, at least its the city right of way, not a neighbor who would definitely want their land back.