We don't know Binance was hacked. Relatively few people use API keys to trade and every reported account had API keys on it. It's likely some malware that looks for API keys in config / python files laying around.
That's not a very sophisticated hack, but it's technically a type of hacking. In the same way that if you leave your keys unlocked in your running car overnight and someone gets in an drives away with it, that's still theft.