Two narrators may transmit from each other while differing so significantly in generation, seniority, or rank that they are not peers in the relevant sense. Reciprocity alone does not therefore make their relationship mudabbaj.
For example, an elderly teacher may learn an item from a younger pupil, while that pupil had long studied hadith with the teacher. Both transmission directions exist, but the relationship is more naturally examined under senior-to-junior narration. The peer condition needs separate evidence.
Mudabbaj requires affirmative answers to two questions: Are the narrators peers? and Did each narrate from the other? Losing either condition prevents the classification.