Sorry but I don't know how to change this into a proper PR.
On the statemanager object the doc says "errorOnUnhandledEvents" is a property of the statemanager. The actual name of the property is not plural, but single: "errorOnUnhandledEvent"
If set to true, errorOnUnhandledEvents will cause an exception to be
raised if you attempt to send an event to a state manager that is not
handled by the current state or any of its parent states.
Github makes it super easy, especially for documentation: go to https://github.com/emberjs/ember.js/blob/master/packages/ember-states/lib/state_manager.js and click "edit"
Thanks, easy indeed! Made it a PR, closing this issue