Public drinking in Ireland forbidden?

My friends and I regularly meet at Eyre Square and drink some cheap cider or beer at night. But when Mara and I were sitting on the grass on Eyre Square and were drinking our cheap Lidl cider one night, the police (in Ireland it's called "Guarda") pulled over and told us that drinking in a public park is not allowed and that we should throw our cans away. Of course, we instantly told them that we were German and that we didn't know that although I think I have heard about it before. Well, but our cans weren't empty yet, so after the guarda was gone, we moved to another part of the park and downed our ciders. The next day I asked Paraic about this law and he told me that you usually have to pay €100 if you are caught drinking in the public. So, I would say that the guarda was really nice to us and that is why we still haven't given up that bad habit of drinking on Eyre Square.