Not using a passphrase decreases the complexity and points of failure of the setup, which he values more than outright security, since a complex (secure) setup is useless if you forget or lose access to the details, and is best left to advanced users, or the company he works for - wink. 

He's writing to the masses, where an XOR'd set of seed words lets you have a simpler setup, easy to restore, and also includes plausible deniability since each of the XOR seed plates is a valid set of words by itself. An attacker has to know it's one of a set to know there's a larger wallet elsewhere. 

The seed+passphrase setup is similar, in that you can load funds onto the seed-only wallet, and you keep the passphrase safe for the "real" wallet. But an attacker now has your entire seed phrase.  

 Thank you for your response. Here my comments to that:

1) Passphrase and SeedXOR have similar complexity. I understand the point, that more complex solutions increase the risk of loss due complexity. Anyhow, that has nothing do to with my question. 

2) Why is a SeedXOR easier to restore? Please explain. 
In my opinion Passphrase is easier to restore and supported by most wallets. 
Furthermore the seed phrase of a passphrase secured wallet has the same deceive feature as the seed of a SeedXOR. You can load both with „ready to lose funds“ to deceive an attacker. The attacker doesn’t know that a bigger wallets exists in both cases. 

3) what is the difference in the attacker having the seed phrase of a 256 bit passphrase wallet or a seed phrase of a SeedXOR wallet. Please explain.