It doesn't only pertain to web development. No where has this ever really been the case. I hear people tallking about C++ front-ends all the time and have books dating in the 1980s and 1990s which talk about the operating systems front-end which is programmed in C. It's just that when people post job descriptions for C++ jobs, they usually just called it "C++ Programmer" because there is not really any structural difference to the language knowledge. In web development, there is because front-end is known to consist of HTML/CSS/JS whereas back-end can be something completely different.
You're probably talking to people who have only done web development, are new to programming, or are in their own little high-level abstraction bubble.