That sounds hokey to me! Admittedly, I don't have the real answer though.. You might go online and see if anything is posted there. You may even see if there is somebody else that can answer the question. Last time I called a municipality about detecting, the first person I got had no idea what I was talking about! Literally I had to explain what metal detecting was! She was nice though and sent me to a person who promptly told me 'NO'...but she was WRONG! Finally I got hold of a person who knew what I was talking about and told me that there were some off limits places and what they were, then chuckled a little and said I could go to the other places as long as I didn't tear the ground up and leave a mess. I made sure to write down that person's name, but even so, I didn't go where I knew I wasn't supposed to!
As much as we hate to be too specific and even MENTION digging, if they have a general notion that you're looking for something in the ground, they may just be under the impression that you're planning on using EQUIPMENT to do that digging, not just a hand trowel! It's hard to strike a balance between saying too much and making sure the person understands exactly what your intentions are. Keep in mind also that if they don't know what the real answer is, they may just say 'no' to get rid of you! It seems like the permissions end up being a small research project of thier own..