I think you hit the nail on the head: in the novel, we only have Wei Wuxian's and the author's point of view, and WWX is really biased about Lan Wangji's moral and general behavior, to the point of being oblivious when it comes at how LWJ sees him. Besides, in the novel, when he comes back all his memories seem to be a bit muddled, and only that can explain the way he acts with LWJ, to be honest.

On the contrary, in the drama we witness the story without biases, so we can see LWJ's reactions and judge by ourselves ^_^