code-server has no default directory unless you passed it on the command line, for example code-server /home/coder. If that is what you did, then you can change that to something else.

code-server also remembers the last directory, so if you opened /home/coder once before, that could be why it is opening by default. If you open a new directory or close that one (File > Close Folder I think), then it will stop opening. Or you can use the --ignore-last-opened flag.