As a follow up, here you can find the Soliloquywp web site terms and conditions. About a third of the way down the page you will find the paragraph:
SoliloquyWP WordPress plugin is licensed under the GNU general public license (http://www.gnu.org/licenses/gpl.html) version 2.0 or later.
Other provisions of the terms and conditions mostly refer to access to support for the plugin, as well as use of the web site, etc. I believe this implies that there is not a split license for this plugin.