Hi Daniel,
That’s an error I’d say. It’s expecting you to travel via Upminster and Romford, which is fine if you don’t want to leave the station to walk, but there ought to be alternative fares for each of the two OSIs with the Elizabeth line, especially since it’s the same train from Barking Riverside. The one you took would be zone 4 only while the other one would be zones 3-4.