Just read about this, technically this is only a DeFi-based hack, as opposed to a DeFi hack, as the smart contract wasn't even exploited.
Hackers exploited a vulnerability in the UI of the DeFi-based website. It should really be labelled a website hack, but nevermind.
Is it really a hack when users are asked to give control of their account over to hacker, and they sign to this ? No really imo.
For example when an exchange get's hacked and loses it's BTC, is it a Bitcoin hack or an exchange hack ? Exactly.
It's literally a contractually binding agreement to lose all your money 
Good lesson overall in staying away from DeFi though...