As best I can make out the book is only autobiographical insofar as sense is concerned rather than any accurate recounting of actual events in his life; it is, after all, a novel and the author has a free rein insofar as not sticking to the truth is concerned, and free rein away from the truth in order to carry his story and his propaganda (I am not trying to be nasty in saying "propaganda", it is a term Blair himself used). It seems generally agreed that it is exaggerated and from what I can find of Burmese history that is so; as part of that exaggeration it is also selective in where his criticisms are directed as I will, from my own point of view, elaborate on below.
Orwell was in Burma from 1922 to 1927 so this was before the time of the British Colonial Service and in fact, even after the Colonial Service came into being, India (and hence Burma, and what is now Pakistan and Bangladesh) was never administered by the Colonial Service but by the Indian Civil Service which was responsible for its own recruiting of officers from both locals and expatriates (often Scottish, not just English, in the case of Burma). By the time of Indian independence approximately 1/3 of its officers were locals. But in fact Burma was split off as a separate colony before then late in the 1930's with an elected government and much control in the hands of the Burmese; that all turned to custard leading to riots that the British had to quell.
Orwell seems to me to have been quite mixed up by his experience (he says himself it almost sent him mad), and in my opinion some of his essays are worth a read, especially ones reflecting on his experience in Burma where his own contradictions and the influences of the behavioural expectations of the locals on the officers are apparent. For example, in
Shooting an Elephant he talks of feeling like bayoneting monks and of the pressures of the locals on him to kill the animal, and in
A Hanging laughing with everyone over the behaviour of a condemned man (both written years after he left Burma). Contradictions of this type, but not the events themselves, can be seen in Flory, for example.
There are things about Burma that Blair does not tell us about and one wonders why; I can only assume because to do so would have watered down his exaggerations. For example, Burma was an imperial totalitarian state before the British took control after the first Anglo-Burmese war; it seems strange to me, given Blair's detestation of imperialism and totalitarianism, that he only mentions all of the ills of totalitarianism with respect to British imperialism. In fact, after the British left, Burma quite quickly reverted to being a totalitarian state again, a socialist one, and became an economic basket case that could not even feed itself. He also does not mention the history of troubles among the various ethnicities native to Burma, but again limits himself to troubles against the British.
In my own view I think it is too easy to be critical of these people, whether the colonisers or the colonised, but has to be seen as within the accepted beliefs and societies of their own times. After all, in future years we will be judged ourselves, and then even the best of us may be seen as being not very nice people when set against that future society's expectations, whatever they turn out to be.
I have worked in a developing country made up of multiple ethnicities and with differences between them; the necessary dynamics of the relationship between expatriates and locals is, in fact, quite different to that which one would like to imagine from our own cosy viewpoints at home in western society. One has to make ones own place in the environment in order to gain respect. I managed because my wife was of one of the local ethnicities (but from another country), and the expatriate manager who I did the assignment for made his place, despite being a normally generous person, by being an abusive brute (and he had the machete scar across his buttocks to prove it); he was both respected and liked very much by his employees (one of whom saved his life).
We can be as critical as we like about the British colonialism and its faults, but in the end India, which had a different and stronger history prior to the appearance of the British (predominantly through domination of the North by a Muslim sultanate which also forayed into the south) than Burma did, has maintained its British administrative and parliamentary systems and English is the official language with Hindi.
That is my take on it, I may be wrong but I think that Blair was inclined to over grind his axe in fields he did not know much about--economics and political science--but was very good at telling us with a narrow parochial perspective what he does not like within the aspects of society those fields play in (a fault that is, it seems, not uncommon among artists). Of course, I may suffer from the same fault too
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