Brutalism is a word that means something when it comes to architecture, and is just used as a catchy word for hipsters in webdesign communities, there is nothing more to that, it's yet another design fad like "flat".
There’s more to it. The philosophy behind the architecture (functionalism, simplicity, and keeping the raw material’s appearance instead of hiding it) maps very well to a philosophy of web design. The main difference is that “raw” now refers to (roughly) the HTML code rather than concrete. The other points, simplicity and the utilitarian character of the layout and of the underlying code, and buttons that look like buttons (analogous to doors that look like doors) are very similar.
