If you don't want to use Instagram, that's perfectly fine. Just don't pass judgement on those who do, that's all the above poster is saying.
The above poster was saying there is a subculture of people who, in order to feel superior, conspicuously avoid posting on Instagram about a sunset. This is an absurd characterization. There is no place in the galaxy in which it is conspicuous to not post beautiful things to Instagram. I have no judgments for users of Instagram, but a pocket full of confusion for someone who assigns a motive and subculture to everyone who doesn't live their lives exactly the way they do. It's provincial and sad, ironically so, considering that in context, that these people are documenting the travels to a foreign land.
Oh no! I guess I became a hipster! Please, I'll download Instagram, I'm not trying to be snooty, I'm just a guy. I appreciate things like sunsets, I didn't know I had to share them. Most places have sunsets. Maybe I can tweet that you should look at your own? No, to be safe, I'll post an Instagram every day. That way I won't be seen as condescending by random people on Hacker News.