I worked in a restaurant, a store and other places.
I have gotten nervous about paying customers staying later at the parking lot & hanging around where their cars are.
It's human nature to be nervous especially when you are an employee.
You don't want to be ganged-up on or leave your workplace wondering if it is going to be robbed & defaced.
Put yourself in a hearing person's shoes at night leaving their workplace and seeing a few deaf people signing. The hearing person doesn't understand ASL. Naturally the hearing person is now out of his/her comfortable environment and feels threatened.
To be able to feel comfortable all over again, they have to call the police. After this whole thing happens, some hearing people will degrade some deaf people to feel better all over again.
This is too bad that this has to happen.