Anyone here a Muslim? Question about culture for you.

My job is about customer service, and I on occasion will have to walk around/open doors for people.

I had a customer recently, who was from Kuwait, who did not want to walk through the door I was holding open for him. I am just curious as to why. I was not/am not offended, and want to make sure I wasn't offending them. Customer was nice, but our cultures are clearly very different.