Guys confuse me

Yesterday I went to a singles mixer event and saw two guys staring gazing at me for a moment not just like loom really quick but like checking me out it appeared. Anywho I had a little alcohol courage and went to say hi to them at different times to each guy and try to start a conversation but they seemed uninterested in our chat so I just left it. I felt really awkward going up to them because I thought they were interested in me. Anywho has anyone ever had this happen to them or have any of you guys down this to a girl and why?