Yes you got it. I think what it is, is you hold the coat so it is easier for the lady to slip into it - from the back and at the height level where it is easy to slip her arms in. When you hold it open, she will move her arms either left or right to what is natural for her, then like mismi said pull the coat up.
And if you kinda not line up (I've had this with my husband even after many years) you kinda don't get insinc - then you sort of joke about it. Either way it is a nice gesture and most women appreciate it.