Remember: the plural of "anecdote" is not "data."

Here we have a single programmer -- about whom we know very little -- and his personal experience. It says nothing about the state of the industry as a whole

My personal experience, by the way has been precisely opposite: my open source experience has led to more job opportunities, easier interviews, and more career freedom in general.

But again, that's just another anecdote. The only way to draw a conclusion like "open source experience is overrated" would be through a study that pits potential employees with open source expertise against those without.