Question

In a hotel, a man was sleeping when he heard a knock on the door. He shifted the blanket and stepped down from the bed. He waked to the door and opened it to find a stranger standing outside.
Upon opening the gate, that stranger said, "Pardon me, I must have made a mistake. I thought this was my room."
The stranger then walked the corridor and climbed down the stairs. The man closed the door and immediately called the security. He asked them to arrest that stranger immediately.
Why did he asked them to arrest that stranger? What made him suspicious?

Answer 1

Because no one would knock at the door of his own room

Answer 2

Well in hotels people are given keys for their room. If it was his(stranger's) room then he must have the keys and wouldn't have the need to knock the door! There was surely something fishy about it!