The metamodel does not require Outcomes to be Produced by a Capability. Such Outcomes are used to model events that occur outside the capability map of the business, such a customer requesting to purchase an item the business has. The BACM metamodel does not have a way, other than an annotation, to indicate that the source of an Outcome is a Performer(Customer). An alternative approach would allow the customer to have capabilities that would produce such outcomes, but this would add model complexity with little benefit other than providing a connection between a Customer and an Outcome. Note that if BACM11-22 is adopted, outcomes are used to trigger value streams and such a connection between Customer and Outcome becomes critical.
If such a relation is added to the metamodel, it should have a plausible interpretation when used to link an Outcome to a Performer that is in a Role with the Capability that produces the Outcome.