every RC diocese has a Diocesan Marriage Tribunal to deal with dissolving marriages. The RCC prefers anullments, however they also issue divorces
Not quite. Canon law clearly states that a marriage that has been validly entered into and consummated may never be dissolved by anyone under any circumstances, and remains in force until the death of one of the spouses.
Can. 1141 A marriage that is ratum et consummatum can be dissolved by no human power and by no cause, except death.
A marriage that has been validly entered into CAN be dissolved if, and only if, it has not been consummated. For example, if the husband becomes incurably impotent after marriage, but before consumation. (A famous example of this was the dissolution of the first marriage of Lucrezia Borgia, the daughter of then-Pope Alexander VI). It is possible that your friend was called upon to help with such a rare case, but much more probable that he was involved in an annulment.
Can. 1142 For a just cause, the Roman Pontiff can dissolve a non-consummated marriage between baptized persons or between a baptized party and a non-baptized party at the request of both parties or of one of them, even if the other party is unwilling.
Provided that the rather stringent conditions for dissolution are met, the decision to do so belongs to the Pope alone. No one else can grant a dissolution. The Diocesan Marriage Tribunal only decides if the conditions have been met, and, if so, prepare the request to be sent to the Pope.
Once a valid marriage has been consummated, though, even the Pope is powerless to dissolve it.