I don't take immediate issue with the points made here, but I think the conclusion is not entirely correct. Security isn't full, it's just harder and more competitive than people think.
I'll explain: because of the hype described here, many, many people decided that security would be a great way to make a living. They were told that there was a severe need for security professionals, and that there would be high-paying jobs just waiting for them to apply.
So these people studied security in school, maybe took the Security+ or CEH certs, and applied for jobs. Those that got jobs got laid off (again, mentioned in the article) when times got tough, or never got a job in the first place. Why?
Security is a field of people who love what they do. Go to DEF CON -- or even better, small, regional infosec conferences -- and you'll find people who are extremely talented... some of whom don't even work in the industry. For people like this, there is a talent shortage.
I've been consistently hiring security people for the last 15 years. There is absolutely a talent shortage at high levels of the industry -- but it's really hard to get to that level. Learning the OWASP Top 10 and a few nmap flags isn't going to cut it.
My experience may not be universal, but this is what I've seen over the course of a lifetime in infosec.