This scenario is to some extent a little bit common but where the failure comes in is where a phone call did not make it so the staff woke up. Also the front door should have been locked in my opinion but at some point someone else would have either come or gone and if someone wanted to get in they could have.

I am surprised OP did not confront the manager upon returning to the hotel for the remainder of their stay. I am also surprised OP did not arrange not being charged for the room upon returning to the hotel for the remainder of the stay. This sounds like a hotel with some serious security, service, and communication problems to not pro-actively resolve the matter with OP. OP shouldn't have even had to ask once giving the reason why they did not stay the first night. If anything the hotel owed him a night comp for his trouble.