Probably related to Syscoin's issue, who tweeted there has not been an issue on their side. Likely that some Binance API keys were compromised, and the hacker traded some of his Skycoins for stolen bitcoins.
Please, everyone, we still don't know what exactly happened so don't get your pitchforks up. The API keys could've been compromised due to an error in Binance's system but also due to relentlessness of whoever owned them.

I'm just surprised that this trade wasn't detected and prevented by some automated anamoly detection. I know these systems are never perfect, but an outlier this huge really could've been found.