Right. But since many parishes have regular Saturday evening Masses around 5 pm, most traditional nuptial Masses are held earlier in the day on Saturday (often around 2 pm or so). Masses held this early are generally not considered “evening” on Saturday, and thus do not fulfill the Sunday obligation (though sometimes priests celebrating such a nuptial Mass will give a general dispensation to the wedding party). Also, Catholic weddings can take place outside of a Mass setting.
FYI, in many parts of the world, Catholic wedding vows are simply exchanged within a regularly scheduled Saturday evening/Sunday Mass.