Attacked at a cemetery

Today I went with my mom and my boyfriend for a walk around our new neighborhood and to a cemetery nearby. My mom just came for a short visit from another country so everything was super interesting to her. She took a bunch of pictures of different graves because they were genuinely pretty with all the flowers and such. We didn’t do anything disrespectful though or behave loudly.

As we were about to leave the cemetery, a man in his early 60s dressed in black (I assume a mourner) approached us with a phone in his hand (most probably filming us). He started screaming that we cannot take pictures here, that we had to leave now and told my boyfriend that he’s seen him here before wearing a tshirt and walking around (impossible - just moved here). He also said he’s somehow connected to the police. My boyfriend repeatedly told him calmly that we were just leaving. The man kept walking behind us and crossed the street with us. That’s when he slapped my boyfriend in the face and pushed my mom who just managed to turn around (a small 60 year old woman). Luckily no permanent damage was caused to either of them, although my mom said that her back did hurt for another 30 minutes or so. There was an older couple walking by who saw everything and didn’t react. They kept on walking and pretended not to hear when we asked them to stop so we could ask if they knew that man. We did not try to fight back to not escalate the situation. We didn’t call the police as we have no evidence and my German is not nearly good enough to talk to the police yet. We were also worried we were in fact in the wrong.

I guess my questions are: is taking pictures of graves frowned upon/illegal? Does it sound like we did anything else wrong? Could the guy try to use that video against us if we did in fact do anything wrong? We just moved to a new city and I am genuinely concerned that he might try to hurt us in the future in case we run into him again.

Edit: just learned the man also threatened my boyfriend not to go back there at night (or especially at night or something among those lines) or he would kill him (or us).

Edit2: I read online that at this particular cemetery it’s prohibited to take pictures except for private use. My mom only sent the pictures to me (to look if the guy was in them) and my grandma. I assume that falls under the private use category but please correct me if i’m wrong.