As others have said, it's basically substituting a big lie for a little lie. You basically told your boss that you're looking to leave in the immediate future. What Reid is talking about is more of a "some time in the possible future I'm looking to expand beyond what I'm currently doing here". When it's framed that way, the current company can keep that in mind and include you if something comes their way that matches what you wanted to move on to next.
Basically, when in doubt, be vague.