If a man walks behind a woman does it have any meaning?

We approached the doorway from different directions exchanged a few pleasantries and exited the building. While we walked to our cars we chatted but he walked a couple of paces behind me. I had to talk over my shoulder to him a few times. Why did he walk behind? We do know each other and have been known to flirt.

I've noticed that he does this all the time.
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He does it to all his female friends. I always thought he was a bit shy!

If a man walks behind a woman does it have any meaning?
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