Dogs will generally go to the largest human in a group. It’s not really affection as such, just evolutionary pack behaviour.
So just nuero chemical reactions? 
Aren’t all decisions that?
It’s logical for animals who have awareness to gravitate towards the largest. Humans do it, too. You alpha males need to be aware of this when checking your privilege.
Some people believe so (materialism), some do not.
It begs thhe question of free will and sense of morality if it is just that.
Free will as opposed to making a decision and then justifying it afterwards?
Let me think about that for a while.
Dogs are shown to produce love hormones when interacting with humans, especially when looking into their owner’s eyes. So they are indeed feeling happiness when they are playing with you. Still maybe not 100% but how can you prove this beyond doubt?
http://science.sciencemag.org/content/348/6232/333
You mean dogs speak Chinese 