sigma nu

I got a call back for Sigma Nu's "Closed Event". I'm uneasy about it because I only went to one event and spoke to maybe 3 or 4 of the guys, didnt really get that involved in conversation but yet still got a call back. I don't know if they honestly are interested in me or just picking people because their "Traditional" event is sooner than planned. Thing is another fraternity that I am interested in is hosting an informal event during the same time and I would like to meet more brothers, not just 3 or 4 like I did with Sigma Nu. Should I go to meet more brothers or is it normal that meeting that few number of brothers and only going to one event still raises enough interest to get you closer to a bid???