Hence why you shouldn't keep large amounts on anything Defi related. Keep it cold storage and when you want to actually trade, then send the funds and when you are done send them right back. Keep everything in Ethereum COLD storage.
DeFi is not just limited to trading our funds in a decentralised manner but its major aspects are staking where traders lock enough assets due to great to average returns being provided according to the ratio of least to highest TVL (Total value locked) in it. Let's think for a moment that you have staked your funds on Binance Dex and it gets hacked, was it your mistake? I guess no, and the funds gone will only be recovered either if the hacker agrees to send them back or is spotted/caught by police.
Maybe his point is that we shouldn't blatantly trust our money to his whole Defi as there are a lot of loopholes that cyber criminals are going to exploit over and over again. So still there is some mistakes if you believed that your funds are going to be safe with them.
And even if there are bug bounty or even 3rd party who look at the code and says it's good to go, sooner or later those hackers are going to find something in that code as they are one step of the game. So there is also risk, a very high risk that everyone should know. And if they are comfortable with it, then by all means invest and locked your funds and hopefully you will get a good returns after the lock in period.