Not sure what particular tools, if any, that site is built with, because it's behind a CDN, but you could probably build it with SquareSpace (I'm not too familiar with the platform), and definitely with WordPress if you know how to use it.
Squarespace offers designer-friendly templates that are easy to customize. WordPress gives extensive flexibility with thousands of themes and plugins to tailor the site. I believe both are great choices for building sites like the one you linked. I have a general suggestion here. For showcasing design work in a style of the website you gave as an example, I think webpage screenshots would be a good choice. They give potential clients a clear and professional view of the projects. You might need a screenshot api for capturing high-quality screenshots of the websites you want to feature. It makes a difference and ensures the designer's work is presented in the best possible light. At least that's how I usually do it for similar projects (in case it helps, I use this screenshot api and I would definitely recommend it).