You are misrepresenting that quote. That comes after giving a fairly generic overview of both in which someone could form an opinion. One does not need to know the peculiarities of Bayesian reasoning to have the opinion "you should incorporate prior knowledge". Also, the set notation does use curly braces.

In my mind you cannot be frequentist or Bayesian after reading just the first paragraph of Chapter 2. But fair enough I am a bit too critical here.

Also you are right, set notation does use curly braces, I am relieved :-). I was confused by the A = [-1, 1-1/n] (interval set notation) on page 8 that I misread as [-1, 1, 1/n]...

> In my mind you cannot be frequentist or Bayesian after reading just the first paragraph of Chapter 2.

I don't think the author is asking you to, at all. They are pointing out that there are two "camps" and you will see these terms bandied about (e.g. if you google stuff). But then they claim (rightly, I think for an intro like this) that it doesn't really matter for the material to (immediately) follow and you are better off focusing on more fundamental ideas of probability.