I mean, being real, I'd be less worried if it was some random dude.

But, whoever called that in just saw some dude in dark clothing fucking around. Unless you get the right line of sight, you aren't going to be able to see the few shiny bits on the typical dark blue uniforms. Especially not with a flashlight bouncing around, while you're looking out a window carefully.

Frankly, if a cop isn't wearing something bright enough to be seen through a dirty window and it be obvious it's a cop, it's on them if someone sics an angry goat on them.