Personally, i would use the term “oblivious” or “ignorant” for more synonyms go to thesaurus.com :)
Showing that Sergei considers the goldfish to be his friend, there does not seem to be a conflict with the relationship between the two. And, yes. It can be called a friendship because any two living organisms can be friends if there wanted to.
It means choose your path wisely and don't be tempted by the things around you. Temptation can be sweet but can also lead you down a dark path.
I have never read what you are asking, but just by looking at it, I would assume that he is stereotyping Dutch people, because he is calling Black Dog an insult, which is "son of a dutchman".
