I think maybe "incorrect" was the wrong word for him to use, since obviously you're free to use whatever you want to get your job done, but otherwise I think his point is valid. If your definition of a "professional" tool is just that some people use it to get work done, then that renders the whole definition of "professional tools" useless, since I'm sure for pretty much any given item or piece of software, you could find someone who uses it for work. Pick the cheapest brand of wrench that money can buy, and there are bound to be some people somewhere using that brand of tools to do paid work. By your definition that means those are professional wrenches. Or if I sometimes use my $5 pocket knife to get some electrical work done at my job, by your definition it's a professional tool, and I'm entitled to blame the manufacturer if it doesn't turn out to be well suited to professional construction work.
I think it makes more sense to define "professional" in regards to tools based on what the manufacturer's intent, or at least claimed intent, was, not on how some users use it. If the manufacturer's stated intent was for a tool to be suitable for professional work, then it's a "pro" tool and it makes sense to judge it based on its ability to support its intended profession. Otherwise it's not a professional tool.
That said, iWork is a bit ambiguous in my opinion. Since the name of the product includes the word "work", it does seem like Apple may be implying that it's suitable for professional work. That said, looking at the feature set and marketing for iWork, it seems clear to me that it's intended more for home users or light work duty, and certainly not for people who's livelihood depends primarily on writing or number crunching or data processing.
