I realized today that I mooned a lot of people when I was in high school. I'd say that just about all of my friends and family got mooned at least once, sometimes more if they were "lucky." And I didn't discriminate against gender either. My female friends got the ojo negro just as often as the male ones. (Due to its controversial nature, I won't take the time to explain the term "ojo negro" here. It's a joke between my brother and I. If you are truly curious, then look it up online and use your imagination.)
But I took the moonings to be a way of expressing my comfort with you. It was like an initiation into the group, if you will. A way for you to know that you were accepted into the "inner circle" (pun intended).