I am not saying to like him. I am making the point that normally PewDie would never make a comment like that. However, considering the subject matter of the video, it makes complete sense he'd make such a comment. He shouldn't have made the comment, but what they set out to do would make anyone angry should they be in the same position. Again, it was an over-elaborate group effort made to hurt him.
Sympathy. Many of us have experienced talking or acting as we would, passive for the most part, only to be suddenly shown anger or hatred for what was done. The clips they used, he was not trying to be annoying. He wasn't trying to be terrible. He was being as he would normally be. They picked out clips and over-dramatized reactions against him. He organized a large group of people to do this, with the intent to hurt him.
Actually, that made me think of something: Would adults really make a video like this? Surely this isn't acting like adults to coordinate and centralize a large sum of hate against someone who is just making YouTube videos. Adults, people who understand they don't need to care, would withhold their opinion instead of going out of their way to create something like this. Again, this is just YouTube. It isn't like he is harming people - as I'm sure you know, he enters competitions just to donate the money to charities - and I know that can't say a lot, but he isn't trying to be a terrible person.