Can people see your message that you sent them on Facebook if you are not friends with them?

I sent a message to a guy and I don't if he can see the message. My co worker sent me a message before I added her as a friend and I saw her message. Why can I see her message before I added her as a friend, but the guy can't? It has an arrow by the messages. Does that mean he didn't see it yet?
Update: There's a check mark and says seen 2:22 PM. Before he told me that he couldn't view the messages before we became friends on Facebook. I didn't add him as a friend yet.
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