Как вы понимаете смысл этой фразы:"To his dog, every man is Napoleon; that's why dogs so popular. "

Для его собаки, каждый мужчина Наполеон; поэтому собаки так популярны.

I think this phrase means that dogs are the best friends of humans they see in us their leaders (owners) dogs are very loyal to their owners like Napoleon's army were loyal to their leader. That's why they are popular.