Animal rights do not seem to be an issue at all in this text. Does this surprise you or not?
I would certainly agree with you that George Orwell does not seem to be concerned with animal rights in his essay "Shooting an Elephant." If I understand your question correctly, you are wondering if we should be suprised by this.
I do not believe there is any reason to be surprised at this. Orwell's essay first appeared in 1936. This was long before animal rights of the sort (some worry about today) appeared as an issue.
There was some amount of concern about animals in those days, but it was generally concerned with the treatment of pets. The idea that hunting wild animals was wrong (which is still not held by a majority of people) only started to come around during the 1960s.
You are right that Orwell does not seem to have an emphasis on animal right, but this does not surprise me, because people are only products of their society. If the society in which Orwell lived (earlier part of the twentieth century) did not care about animals and their well treatment, then why would his lack of concern be surprise? All societies have blind spots. One can argue that things have not changed much today with alligator shoes, mink coats, etc.
In short, I am not surprised, but I am not too judgmental, because of the sociological factor.