Open source software has existed long before the invention of the (D)VCS. The author likely hosted a barebones HTML webpage or a txt file describing the project. There definitely was an FTP server somewhere with tarballs. The author may have been reachable by email. If you were really lucky …
Android is also open source, but I do not want all open source software to become like android. What makes most open source good is not just the available source code, nor just the software freedoms, it’s also that it’s built openly, by the users. So please don’t turn issues and PRs off.