This is the same sort of claim as everything is water, the four elements, matter, mind, math, or according to this article, information. The difficulty as always is showing how everything is actually X. It started with Thales or Parmenides, and the allure of reducing everything to one substance remains with us to this day.
Except physics is precisely not a substance. So let me ask that again, what else could information be? Even dualistic philosophies are conceptually reducible to "physics" because physics is all there is, by definition. To paraphrase George Carlin about the Earth and plastic, even if you think "minds" or "information" are not "physical" (by which people usually mean material, which is yet again something else), then redefine physics to be "old physics"+"that new arbitrary thing you named" and you'd still have physics.
Those discussions might involve interesting physics, but it's certainly clouded in very poorly chosen and confusion-inducing terminology.
Physicists certainly don't concern themselves with the study of everything. Take sociology or art, for example. At best you can you say everything is made up of physical stuff.
But even then, there are questions. Are math and logic made of physical stuff? What about causality or laws of nature? And what of universals or possible worlds or counterfactuals? If those exist, are they physical?
And then there's consciousness, and the ideas we have about the world, of which the study of physics is but one domain (containing concepts of energy, mass, fields, laws, information). Are these ideas physical?
What about the debate over the proper interpretation of quantum mechanics? Is that physical or philosophical? Is philosophy physics?
You quickly run into problems when you say that everything is domain X, because then you have to justify lumping everything into that category.
And the idea that everything is physics is open for debate, so clearly not everyone agrees that it is true by definition. Most things in philosophy don't get a free pass by virtue of definition, because people aren't going to usually agree to go along with said definition. Instead, they will want to ask what it means for everything to be physical.
That the discipline of physics doesn't study everything doesn't entail that everything isn't physics. The title of the OP doesn't refer to the discipline.
As for your other points, I'm familiar with the debates on physicalism in their various forms. I just believe most of them are elaborate semantic games with very little actual content.
That people will ask what it means for everything (or anything) to be physical is precisely my point — stating that "information is physics" is a vague and (in my view) probably empty/tautological statement if you don't explain what you mean by that more precisely.
