Google's definition is "a person who follows the latest trends and fashions, especially those regarded as being outside the cultural mainstream." We used to call people who followed the latest trends and fashions "trendy". The only difference between "trendy" and "hipster" seems to be the qualifier at the end of the hipster definition: "...especially those regarded as being outside the cultural mainstream." But that feels weasle-wordy to me. It's like saying, "a hipster is someone who follows the latest trends and fashions, except when they don't".
People have been wearing flannel and hats for a long time (check your parents' photo albums). Whether or not the person wearing those clothes considers themselves to be making a new fashion statement seems to be an assumption made on behalf of the person calling the other a hipster. Because of that, hearing someone call another person a hipster has always come across as that person projecting their emotions onto another person, not as a description of anything that's actually real.