I agree with you that reporting selective truths can still be a very strong form of bias. However, Oliver is completely open about the fact that he's entirely biased. It's clearly editorial. (And also clearly a comedy, not a serious news program.) I could still see an argument that the bias is unfair, but in my opinion far more insidious are organizations like Breitbart (and I'm sure some left-leaning ones as well) that use this selective truth-telling to serve their biases while making an effort to appear unbiased.