What does this make me?

I was walking back to work on Saturday after my lunch break. I walk the same path every day because it's the shortest one.

On this particular day I heard a black woman scream (I wasn't sure if it was screaming at first) and saw a black man holding her from behind. I thought he was hugging her. It became apparent very soon that he wasn't hugging her, he was busy mugging her. This all happened in a side street about 200 metres (600 or so feet) away from where I was. He was trying to steal her bag of groceries.

I remember standing still for less than 2 seconds and staring at them and, in my mind, various scenarios were playing out.

What went through my mind was:

Do I start running toward them, shouting and possibly scaring the mugger away? I am a big guy with a manly voice so it might have happened. But what if he didn't run away? I'm a fast runner, what if I arrive there too quickly and all of a sudden he pulls a weapon on me? I could beat him up possibly and be a hero... or something could happen where he either injures or kills me or the other way around.

There were so many things going through my mind during those 2 seconds. Then I just kept on walking to work an acted like I never even saw it.

Does this make me a coward or a bad person or evil? Does this make me a racist because I am white and they were black? Should I have risked my wellbeing and tried to help or did I do the smart thing by just staying out of it?