Basically you can setup your outlook add-ins one of two ways for your users. Either let them explore and download whatever they want through the store, or you as an organization choose and select "approved" add-ins for them.
If you follow the screenshots from the second part of that article, you will see there is an option there for "mandatory, always enabled." With that selected, it will be turned on by default for your users.
The second way you see this approached sometimes is for settings/options in stuff like outlook. In that case, you will need to read up and explore more on group policys. Not necessary in this case, as the O365 portal allows you to do this through its settings, but for more one off/settings type things, group policy would be the way to go.
I am aware on how to deploy the the add-in itself and that actually worked fine.
However, the article you sent indicates that an Exchange administrator can pre-configure you the settings for add-in itself that are normally configured by the user. With the mention of an Exchange administrator I would assume that this does not relate to GPs but something inside Exchange.