DD settled easier for my DH too. Sometimes she went a little nuts with me like a baby animal scrambling around for food (which she was!) so I think smelling the milk or at least associating mama with milk is spot on.

I wouldn't change him at night unless it is a dirty one. If I'm completely honest even then I would only change DD if I knew she had pooed or she was already unsettled therefore was ruling out being upset due to dirty nappy.