BIND 8 and BIND 9 are the same module in Webmin, it is historic that the directory is bind8. It has nothing to do with what’s inside.
It is named that way because BIND broke backward compatibility with its configuration file format when it went from BIND 4 to BIND 8. That meant Jamie needed to make a new module. But, BIND 8 and BIND 9 have basically the same config file format; 9 gets a few new options, but the same format. Because bind was already taken as the directory name for the BIND 4 module, the new one became bind8.
In short, stop looking at URLs, they don’t matter.