There are multiple forms of crying. It's emotional release. It can be a burst into tears, it can be ugly sobbing, it can be a single tear running down your cheek and each and every one of these ways is normal and legitimate.

Forgot to mention, the reasoning can be whatever, too. As I said, emotional release. Could be joy, anger, fear, frustration, empathy. Some people force themselves to contain it, others don't or can't. Some will not feel the urge at all. All valid. I've shed a few happy tears myself in my time, feels really good, actually.