With the code you shown, you get all the plugins of that type implemented by any module, not just from one module. In fact, when I execute the following code, I get the plugins implemented also from the Views UI module.
The module name passed as first argument to
ctools_get_plugins() is used to namespace the plugin type: There can be other modules that implement a "export_ui" plugin type, and that is the reason why the function requires the name of the module defining the plugin type.
See also the description given for hook_ctools_plugin_directory():
This hook is used to inform the CTools plugin system about the location of a directory that should be searched for files containing plugins of a particular type. CTools invokes this same hook for all plugins, using the two passed parameters to indicate the specific type of plugin for which it is searching.