It was probably just full of garbage (which is also “limp” and attracts flies) and the idea of some cop having to cut it open and go through it because you called it in is sort of funny.
With that said, I have wondered about similar things. One time I saw a guy I thought might be dead but I waited a few minutes, he moved a little, and I figured he was probably just very drunk so I left. Another time I did go tell an NYC cop that there was a guy lying on the ground in the middle of a busy street, and the cop didn’t seem to care. Maybe I should have called 911 instead but I didn’t want to be officially associated with the situation.