If there was a hard fork in October 2018, it was probably to remove the attacker's blocks.

I am not involved with anything here, actually I didn't even read the thread before posting. I was just checking out NYC on coinmarketcap, and I checked the rich list on the block explorer. There I noticed 32 blocks that said "Mr.51%", and I was like wtf? Inside these weird blocks is a single transaction with the input as the destination address. The balance appears negative.

Not many people understand what a 51% attack means, it is talked about a lot in the original bitcoin white paper.

Because the block times are fast, 300 confirmations are necessary to prevent another 51% attack.