Trash disposal isn't free, yea the dog poop is probably a negligent amount, but most people have to explicitly pay for trash disposal, and so filling up other people's trash cans can either cause an additional financial burden on them, or mean that they can't effectively dispose of all of their trash.
It looks like in your case, each unit gets a can assigned to it, and service fees and replacements cost the individual directly, additionally, there are fines for trash violations, so having other people put unknown trash in your bins can result in a direct financial burden. I think it's pretty reasonable to be relatively protective over your trash bin if you are the one that has to pay for service, replacements, and fees.
There is a concept called prior art in patent law. Prior art is information about the invention that exists before filing, it can both help secure a patent as well as prevent someone filing a patent for someone else's existing invention.