It might still be. The original metasploit developers had a habit of vendoring all of their dependencies to create a mono-repo that "just worked" (tm), even after Bundler was created, which beefed up their SLoC count. Plus there's lots of miscellaneous supporting code that was added for various past exploits. However, while some see "largest Ruby codebase" as bragging rights, wise Software Engineers will see that as a liability to be avoided.