I believe that comment is being down voted because of its feel and tone. It's a quick one-line complaint with a negative "low-class" abbreviation at the end. It

I believe that comment is being down voted because of its feel and tone. It's a quick one-line complaint with a negative "low-class" abbreviation at the end. It's a little disrespectful to both the ycombinator (who's system is being criticized) and to the person who submitted the video with better luck than you had. People who read a comment like this are more likely to feel emotions of annoyance, mild anger, and contempt. These things happen sometimes, you say something and it gets interpreted in a way you didn't intend. I wouldn't worry about it too much. Probably a better version of this comment would be something like: "I actually submitted this 18 hours before this one went up. It's funny how sometimes they catch and sometimes they don't. Super interesting video though, glad it's being appreciated!"