I ran into this question today. Why or why not? And if not, you’re saying that Linux and Node.js are not professional software?
I think in pretty much all circles “professional experience” means you were paid some money to perform a set of tasks for another person or company. I wouldn’t call myself a professional carpenter because I built a table in my garage.
If a job description says “Requires 2 years professional development experience” I would take that to mean 2 years of being paid to work as a developer. Under that definition, open source would not be “professional experience”.
That doesn’t necessarily mean that when they say Requires 2 years professional experience that they won’t take someone with no professional experience and lots of open source experience though.