I do know what that is, I also know that a Pre Premiere is when either testers watch the movie to say what they think about it before they actually release it or when important people get to watch it first, like actors family members, big sponsors and normal people who had a hard time getting tickets.
Where did you get tickets to it? And where did you see the movie? Because I googled "Deadpool Pre Premiere" and literally nothing came up, it's a big thing, like breaking a record of earning $135 million over its first three days in theaters, so I thought the big Pre Premiere would come up several times, easy on google.