Well it seems VERY likely that Binance users had API keys compromised - that's why Binance suspended all active API keys and halted trading for 6 hours.
Why the price of SYS went to 96 BTC is up in the air. Likely a large group of trading bots, perhaps trading with the compromised API keys (other people's money).
Block 87670 is quite odd. Somebody had access to at least 45 million SYS to create that block. Of course that is possible if they hacked Binance... Nonetheless with these types of hacks, usually the altcoin is just the intermediary currency, the hackers are looking to withdraw BTC in the end. So they pump SYS (or whatever coin) with hacked accounts, then withdraw the BTC.
Just some thoughts. We should know more soon.