The poster used slang to reference the event and someone else was making fun of the slang by taking it literally, completely trivialising the fact that a huge natural disaster occurred which resulted in death, injury, and hundreds of millions if not billions of dollars in damage.

I _am_ that poster. English is my second language and I wasn't aware that the word heavy is perceived as slang. I should've used "serious".

No, you're fine. It was just the reply seemed a little inappropriate.