One of the dependencies is `rod`[0], which is a web scraping/automation library, and I believe requires a browser to work. I don't know what they're using it for though as I haven't looked at the code (and I'm not familiar with Go anyways). There's a feature of the library that finds and installs a browser, but they may just be preemptively including chromium in the dockerfile and assuming that non-docker users will already have a supported browser on their machine.
which for sure matches my mental model of using ttyd and ffmpeg -- what in the world would anyone need chromium for?