Is it appropriate to put your hand on a coworker's lower back?

One of my coworkers did that today. We were talking at the printer, and they put their hand on my lower back when I collected my papers to leave. Not just a brush either—which may have been on accident. It felt like their hand was right above my belt, and it lasted a few seconds. They behaved like it was just a regular pat on the back/hand on the shoulder, so I did too, but it felt strangely deliberate and intimate.

We had been talking about our spouses, too, which was probably what made me suspicious in the first place. Besides my wife and exes, nobody has really touched my lower back. I do have a scar down my lower spine and only partial feeling around it, so maybe I'm just more sensitive about that area than average.

Obviously they know I'm married, and they are too. I don't know if they even like men. It just felt weird. I mentioned it to my wife, but we have very different thresholds for touchiness. She thinks that it was probably innocent, I should say I don't like it if they try it again, and I should blame it on the scar if they try to make me seem sensitive because "scars are cool!" So, that's the advise I'm taking, but I would appreciate a second opinion for reference...

Is it appropriate to put your hand on a coworker's lower back?
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