To get back on track, Orwell (in this passage and throughout the entire book, really) is basically dramatizing fundamental means of understanding the past, and the effect this has on how the future is imagined. Yes, it is about dogma, but no, the enforcement of dogma does not necessarily have to be as institutional or intentional as you seem to be suggesting. A fundamental aspect of social existence is that understanding the past draws heavily on our assumptions in the present, which in turn are drawn from how we view the past. Our understanding of the past shapes how we reify the world around us, which in turn influences how we imagine future possibilities.
See [double hermenutic](https://en.wikipedia.org/wiki/Double_hermeneutic), [reflexivity](https://en.wikipedia.org/wiki/Reflexivity_(social_theory)) and [postmodernism](https://en.wikipedia.org/wiki/Postmodernism) (please actually read about what postmodernism is, rather than relying on popular understanding of the term, which is very often inaccurate)
As quoted in the original Command & Conquer!
What's weird is that this was meant to shock, but here we are in 2020 and this seems to be a good idea to a lot of people for some reason. 1984 was influenced a lot by Orwell's observance of Stalinism, where they would edit out people from old photos who had been executed and so forth. Stalin took a close interest in editing screenplays, editorials and even fiction produced in the Soviet Union to make it fit the narratives of Marxism. Why did he spend so much time on all of this? You have to make the whole ideology hang together if you want to transform society. The ruler must remove all contradictions everywhere so that all voices sing in unison one unifying vision and that includes popular art and media. There must be no contradictions!