Neighbor using our trash can

We just recently moved into an apartment complex that has a front door garbage service. They provide a can and you set it outside nightly and they come take it if it’s bagged properly. Ours had two bags and some cardboard in it cause they don’t come on weekends and it’s Sunday. We got home from grocery shopping and found our neighbor across the way put his bag on ours? It isn’t a full sized bag either, just a small grocery bag with some nasty lookin goopy shit in it. I know it’s just garbage but we’re all provided our own can for this purpose, or could even set it outside on the ground out front of the door, so why use ours? I also don’t want to be responsible for his messes, or have someone I don’t know that well getting comfortable around our property ya know? AITH for thinking it’s strange?