that is suspicious indeed. I don’t know if you can determine if some fringes are atmospherically induced or not, but the fact that they are larger than the coherence are makes it quite likely. On the other hand, I have seen wonderful fringes over ice with comparably low coherence.
You can set a low-coherence threshold for the valid pixel expression and see if the remaining pattern over the urban area makes sense. An example is given here Subsidence map in 3d view
Furthermore you can check if there was a rain event during one of both images in weather archies.
Lastly, you can try another image pair and see if the same area is covered by fringes.