One-time pads are probably what they meant to say instead of simply symmetric crypto. One-time pads are unbreakable, but the issue is transmitting the key to the recipient. Public-key crypo is so widely used because it offers a solution to key distribution. But in terms of theoretical security, public key crypto isn't as secure as a one-time pad.
No he didn't mean that. Scheiner constantly talks about how mentions of OTP are a key red flag for snake oil crypto. Yes the math is impeccable, but the implementation challenges are enormous. As this leak confirms implementation is a much bigger problem than the math.
