The AI is a Utilitarian Moralist with Hedonist influences
There are many different mutually exclusive schools of thought about what is or is not moral; so, to say the AI is benevolent means that it uses one or more but not all of these definitions of right and wrong. Russell's 3 principles suggest the likely dominance of utilitarian morality or hedonism as the dominant moral standards of such AIs but makes moral relativism and categorical imperatives against the AI's nature.
Utilitarian moralism at its core means that the right choice is the one that takes the sum of all the good and bad caused by a decision and picks the one that leaves the world as a whole better than all other choices one could make. Hedonism defines morality as the pursuit of things that cause pleasure and the avoidance of things that cause suffering.
Either waySo, the AI's since of morality is based on context rather than categorical imperatives (like saying that lying is either always right or always wrong). If the AI knows that telling someone the whole truth has a smaller chance of a positive outcome, or if it would just cause undo stressunhappiness, then the greater good may require a half truth.
For an example, let's say the protagonist has a thumb drive containing instructions for how to make a vaccine against a terrible bio weapon that will soon be released. The bad guys are breaking down the door, and the AI decides that the best way to hide the data until the good guys show up to help is to swallow the thumb drive. The AI knows every single reported medical emergency in history caused by swallowing similar items; so, if the protagonist asks the AI if it is safe, it must choose between this one man's right to know if it is safe and the millions of people who could die if he does not.
If the AI were a categorical imperative moralist, then yes, it would tell the man about the 0.3% chance of choking to death, but if it is a utilitarian moralist or hedonist (still forms of benevolence), then it would respond with something motivating or comforting like, "You should be fine", "There is no better option", or "If they can't find it, they have a reason not to kill you" because it would see talking the man out of swallowing the drive as the immoral thing to do, even if it could maybe harm him.