That article is pretty worthless. First, he says "clearly the terminals had access to the Internet", and that if they used a private network, it'd not have been a problem. That's just wrong. Let's assume the POS terminals connected via IPSec over a frame relay linkup to several datacenters. A compromise in the processing center could cause an issue. Or, you could attack the POSes and have them record data to some internal site which you can access from another point in the intranet.

Second, his only actual argument is: "Someone probably made an out of process change to Target’s POS system and nobody noticed."

Sure, maybe. Or maybe someone subverted some other security system first. Who knows. Useless conjecture is just that.

Then he goes on about how the NSA should be fixing these issues. Okie dokie.

This is the same guy that doesn't understand how search engines work, and asked Eric Schmidt to manually fix his sister's website ranking in Google. I wouldn't take him as a useful source.