Always switching technologies will get you only basic knowledge in each of them. Going past the surface requires daily use and years of constant evolution. That's how you become an expert in something. Deeper understanding. Not broader.
However I get what you mean. The guy does seem to be a bit up himself.
Always switching technologies won't get you in depth knowledge, but it will show you different, possibly better approaches. I would say a bit of both experience, as well as learning new ways of doing things helps.
I learned Java at university. Inheritance and Polymorhpism were like black boxes until I learned Perl afterwards, and the mechanisms are there in front of you (OOP in Perl is a bit of a hack, but it makes it transparent how it works). That (and other features of Perl) helped my understanding of Java.