Is There a Line for Gentlemanliness?

On Tuesday evenings I take a step aerobic class to give variety to my work out. The other night a new couple came to the class. As typical, we all wait outside the door while the yoga class leaves. This man held open the door, let his wife pass, and then motioned for me to pass. I though, how polite, and went though. What I wasn't expecting, though, was that he lead me though with his hand on my back. I wasn't quite sure what to think of it. I do know that it wasn't meant in any romantic way toward me, but I still wondered why. These are my two conclusions. It's a habit and he forgot that his wife already went in before me, or it is something he does for everyone no matter who. Either way, it is a very gentlemanly thing for him to do. But I ask the question, is there a line for this sort of behavior?

I enthusiastically applaud his courtesy toward his wife and think she must sure appreciate his attentiveness, but do you think his gesture was appropriate for a complete stranger? I, of course, like it when a date or any guy for that matter shows that courtesy toward me, but considering that he is married to someone else kind of make it awkward.

I favor the conclusion that it was just a habit and didn't think anything of it at the time. To which I would hope that other guys treat their wives with such respect and so frequently that it is a completely natural thing for them to do.