CJA: Unexpected Events Returned When Metric Is Filtered by a Dimension

I'm seeing an unexpected behavior in Customer Journey Analytics and would appreciate some clarification.

When I use custom event dimension along with the Events metric, which is filtered with specific attribute (for example, where a specific attribute equals a particular value), the report still returns events that don't appear to be associated with that filtered attribute.

I verified both the incoming analytics and CJA request and the data layer, and I couldn't find the filtered attribute being set for those events. Based on that, I would expect those events to be excluded from the results.

Can someone explain why these events are still appearing when the metric is filtered by that dimension value? Is this related to how CJA applies filters at the event, session, or person level, or is there another aspect of CJA processing that could cause this behavior?