As Rob mentioned, any colony within 3 miles or so could have found it, but the hive next door would probably be first to do so. This is why it's recommended to clean out dead hives as soon as you notice them, because they will quickly be robbed when the weather is warm enough, and bees going into other hives to rob is a primary way diseases and pests are spread. Just keep the entrance on your surviving hive small for now, in case there are robbers from other hives alerted to your apiary. Whether it's your hive or not, removing the deadout will stop the robbing and quiet everything down so you can inspect.