Yes, their first attempt used load order overrides and search patch patching. Now, it uses linux containers to ship an isolated environment. Think of it as more similar to docker (or LXC/LXD). That said, I haven't used it myself to so cannot comment on how difficult it is to use. Most people here are advocating for them permitting proton use without necessarily supporting it officially though. Which can easily be done by changing an option in EAC.