Include Backlog Refinement in the Scrum Events section
Backlog Refinement adheres to the definition of event (formal opportunity to inspect and adapt something.) Promoting it to event would make the guide tidier (presenting everything as a role/artifact/event,) facilitate the understanding and make it more difficult to forget it.
But it would be needed to slightly change the description of event since it states that everything is time-boxed; refinement would be an exception to this rule.
Joshua Partogi commented
It's not an event. It's an activity.