I think he meant to be aware and never really trust an exchange, it's true that this first quarter year around if i'm not mistaken only this turkish exchange that did a rugpull or exit scam but we've experienced such thing quite frequent times from the past not to mention the third rated exchange that we don't even know where those are based on.
There's definitely nothing wrong with using cex more specifically if it's a big 5 exchanges but just don't too trusting to these exchanges I guess, as people have said many times "not your privkey not your money"