German cops want to know why I took pictures of the Brandenburg Gate. As an American, why do I NEVER hear about travel restrictions here?

Like, this place is awesome. I understand it's the center of a major European city, but this is, like, on par with the Washington Monument. I took some pics on my phone and they slowed down next to me on their dirtbikes and gave me some weird looks. I kept shooting, and they pulled over. They got off their bikes and approached me, and I go, "Excuse me?" And they say, "What are you doing?" And I'm like, "I'm taking pictures of the Brandenburg Gate." And they're like, "Nope, you're coming with us." Now I'm across the street at some police station being questioned about why I took pictures of the Brandenburg Gate. What the actual hell, Germany? As an American, I've heard so many stories about strict travel restrictions in the Middle East and China, but I've never heard anything about this. Is this normal? I thought it was just the heat of the moment, but I looked up the laws after the cops left and it's an established thing. Not sure what to do. Anybody experienced this? Please tell me this isn't a real jail. I already had one and it wasn't fun.