When a guy wraps his arm around your waist from the side, what does it mean?

sagigurrl3
I have this coworker that I have a mini crush on. We both have significant others and while we are friends, have never flirted before. The most "touching" that we ever did was a fist bump or high five.

We both are teachers and haven't seen each other for two months. Today at our first day, he gave me a hug. I did not think much of it, but later when we were walking to our cars, he wrapped his arm around me again. I thought that he was going for a side hug, but when I started to pull away, he left his arm around me, so I left mine around him. Mine was around his back and (as another coworker pointed out to me) his was around my waist. We walked a couple hundred feet like that.

Does this mean anything? We both know that the other has a significant other, but I guess that I'm surprised that we went from a fist bump the last time that we saw each other to a pretty long hug/walk today.
When a guy wraps his arm around your waist from the side, what does it mean?
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