Changing a die roll of critical success to a result of two successes

Near the end of the recent BoW report of SoF vs. S&M, pitting Killian vs. Carlos Bostria, Killian rolls a in a combat roll and insists that he may convert that result to . I thought that this conversion is only possible during a switches step and that in a combat roll, , only results in one damage. Please correct me or correct Killian.