This is normal @Skydiver
The LV2 standard packs the plugins in the so called "bundles"
A bundle can have one or multiple plugins and that is entirely a developer's decision. On many of the cases the decision to bundle multiple plugins in a single bundle has to do with shared code.
In the case of the plugin you downloaded, the developer decided to pack all plugins into a single bundle. As the bundle is not divideable, our system only operates the entire bundle, hence the installation of the other plugins.
There are lots of different examples like this on the Plugin Store.