Sunday obligation met??

I was visiting friends for a wedding which was on a Saturday afternoon; they told me that the wedding mass counted for my Sunday obligation, is that true?

The answer is “possibly” depending on the time of the wedding and the readings. Let me explain. In order for a Saturday mass to fulfill the Sunday obligation two conditions must be met. First, the mass must be after 4 PM. Second, the readings must be for the Sunday liturgy (or Vigil readings), this is especially true of the Gospel. The optional wedding readings are not typically acceptable. Since you didn’t mention the time of the wedding, or the readings, it is possible the obligation was fulfilled.

I personally have found such weddings to be rare. Most Saturday weddings are well before 4 PM and they almost never use the Sunday readings. While the local pastor does have some options regarding those under his authority, according to Church law:

Parish priests and other priests or deacons cannot dispense from universal or particular law unless this power is expressly granted to them. A dispensation from an ecclesiastical law is not to be given without a just and reasonable cause, taking into account the circumstances of the case and the importance of the law from which the dispensation is given; otherwise the dispensation is unlawful and, unless given by the legislator or his superior, it is also invalid. (Can 89-90)

I hardly see attendance at a Saturday wedding mass as a just and reasonable cause for dispensing from attendance at a Sunday mass. So unless there were other issues of which I am unaware, I would argue those who did not attend either a Vigil or Sunday mass did not fulfill their Sunday obligation.