Being familiar with academic jargon I think you are simply mistaken, and quite frankly a bit too confident in yourself if you think that you just happen to know something that the entire university vetting system doesn't know.
France and England obviously existed before the 15th century, but I am willing to bet that wasn't what your professor met. I am willing to bet he was talking about France and England as conceptual nation-states which didn't arise until the 15th century. The 12th century England was far different from the 15th century England in political structure and it was evolving into a modern nation state, and the same with France.
This has a lot of backing actually. There were certainly merchants and traders before the 16th century obviously, but a mercantile CLASS which functioned in the context of a society at large didn't emerge instantly and didn't exist since the beginning of time, in fact I would go further than your professor and say that as a class the mercantile class didn't emerge in Europe until the early 17th century ( I would argue that despite great Mercantile influences in Renaissance Italy and 15th century Spain post-Columbus that wouldn't really qualify as a class, though valid cases can be made to the contrary ala Medici-esque bankers ) .
If he does think this (which I doubt) then I agree with you. More likely is that he feels that written history isn't the end all be all of history and that other sources, be them oral traditions or a sociological examination of history, kind of like reconstructing zeitgeists, to be valid. While its certainly okay to disagree with that point of view to varying degrees its not an invalid one to have. It should be remembered that only half a century ago such a viewpoint of examination beyond institutions or "traditional" history was actively discouraged and called "lazy history" , and if your professor is old enough it could be a misconstruing of circumstances, I've seen professors give redundant lectures to history graduate students on the importance of considering economic, social, and cultural history as well as "traditional" history; ignoring that most people don't need to be convinced of that.
Have you actually tried to talk to him and see what he means, or "call him out?" If you are too worried about him lowering your grade because he can't handle criticism try to get him to engage you by asking a question (Socratic Method) " Wait, I thought Modern England came about circa 1066 with the Norman Conquest, what are you defining Modern, or England, as? " or something along those lines. Professors who can't handle criticism and might lower grades for troublesome students usually LOVE to give out information, so this is a "safe" way to handle those professors, though they are extremely rare.