Guys, Why do guys like to walk behind girls on stairs? I know there is an obvious answer but it that the only reason?

A group of friends went hiking and there was a set of stairs. One of my guy friends has a dog that kept trying to run in front of me. I offered to let him go in front of me, but he said he wanted to pause and walk behind. He waited a minute then was behind me again.
Guys, Why do guys like to walk behind girls on stairs? I know there is an obvious answer but it that the only reason?
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