Apparently its a misunderstanding, but Sunoo solos and just other people who don't like Ni-ki thought that it was Sunoo cake and that Ni-ki was bullying him again and being malicious by blowing out that candle.
When it turned out, it was the groups cake, and he was joking around by putting the candle out, using his hand (which is pretty damn cool), but others took it a different way.
Ni-ki even apologized after the candle blown out, and everyone laughed it off..
My thing is this, Ni-ki is my baby and he JUST turned 17 years old, so I feel people should give him a chance to grow up and to make small mistakes (even though this wasn't really a mistake, but a playing around thing).
People forget how young he is, but because he doesnt look young, people dont see him as a maknae and always say something about him, as if he's one of the oldest members.