I take it to mean, Ph.D; not from experience, but that's the only meaning that makes sense in the context.

My read: he just means it in the sense that I mean "professional" when I say I'm a professional application security person, except that it's weird to say you're a "professional computer science" when your day job doesn't involve writing papers.

That's pretty much it.

I got a nice piece of paper, but it's not like my day to day job involves much of what I learned during school.