Orwell is accurately describing how history is recorded. Yes, all history, well-research history included. History is necessarily fuzzy and non-absolute. Historians work in conditions (social/political contexts) that shape not only what records are deemed appropriate to use, but also the means through which history ought to be recorded, presented and publicly disseminated. For example, Herodotus was a historian who relied in hearsay and myth to inform his largely oral depictions of world cultures. This was the accepted standard of his time. Fifty years ago, history was largely told as a series of 'big men' whose impact was absolute and only resisted by other big men. Today, history is largely social history, and uses lots of sources that account for everyday interactions, and the product is typically a monograph and a few blog posts or op-eds.
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)