I agree it's largely culture, but I think there are some technical issues that go with the culture as well (which are sometimes the reason for some cultural elements). Even someone who solidly understands OOP, for example, may not know all the many specific gotchas and possible pain points of C++ if they haven't written a lot of it, and some of the cultural conventions common in C++-land were developed because of awareness of those gotchas, and in an attempt to minimize them. C++ is probably a limit case because it's so large and has so many interacting features that there's a lot of accidental complexity, so just knowing the PLs concepts only takes you so far, but I think many languages have some similar things.
Heck, even ye olde C has a whole litany of detailed spec edge cases you need to know about if you want to understand the finer points and avoid some nasty pitfalls (and an even bigger list if you go to C+POSIX).
Oh, I agree, and we're actually talking about the same thing. We're just defining the word culture with different scopes. My scope was, approximately, "anything about C++ that you really need to know to write idiomatic C++ code and interact productively with your C++ coworkers and community, but which you didn't learn from that Introduction to C++ for Lisp Nerds book that you skimmed last weekend."
Clearly not a hard-and-fast definition. The more "proper" scope of the word culture is, of course, ultimately a giant philosophical issue which I intend to blithely handwave away. ;)
(I suppose one could try to argue that all of C++ is a cultural artifact, and C and assembly for that matter, but sooner or later you'll reach the Turing machine, which if you chip away at it you'll soon discover is just the tip of an iceberg which consists of all of mathematics, and then folks like Plato will turn up on the battlefield looking for a fight and holy cow, look at the time, gotta run.)
Heck, even ye olde C has a whole litany of detailed spec edge cases you need to know about if you want to understand the finer points and avoid some nasty pitfalls (and an even bigger list if you go to C+POSIX).